Note: Descriptions are shown in the official language in which they were submitted.
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' SOFT FILLED TISSUE PAPER WITH BIASED SURFACE PROPERTIES
TECHNICAL FIELD
This invention relates, in general, to creped tissue paper products and
processes. More specifically, it relates to creped tissue paper products
made from cellulose pulps and non-cellulosic water insoluble particulate
fillers.
BACKGROUND OF THE INVENTION
Sanitary paper tissue products are widely used. Such items are
commercially offered in formats tailored for a variety of uses such as facial
tissues, toilet tissues and absorbent towels. The formats, i.e. basis weight,
thickness, strength, sheet size, dispensing medium, etc. of these products
often differ widely, but they are linked by the common process by which
they originate, the so-called creped papermaking process.
Creping is a means of mechanically compacting paper in the machine
direction. The result is an increase in basis weight (mass per unit area) as
. welt as dramatic changes in many physical properties, particularly
when measured in the machine direction. Creping is generally
accomplished with a flexible blade, a so-called doctor blade, against a
Yankee dryer in an on machine operation.
SUBSTITUTE SHEET (RULE 26)
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A Yankee dryer is a large diameter, generally 8-20 foot drum which is
designed to be pressurized with steam to provide a hot surface for
completing the drying of papermaking webs at the end of the papermaking
process. The paper web which is first formed on a foraminous forming
carrier, such as a Fourdrinier wire, where it is freed of the copious water
needed to disperse the fibrous slurry is generally transferred to a felt or
fabric in a so-called press section where de-watering is continued either by
mechanically compacting the paper or by some other de-watering method
such as through-drying with hot air, before finally being transferred in the
semi-dry condition to the surface of the Yankee for the drying to be
completed.
The various creped tissue paper products are further linked by
common consumer demand for a generally conflicting set of physical
properties: A pleasing tactile impression, i.e. softness while, at the same
time having a high strength and a resistance to tinting and dusting.
Softness is the tactile sensation perceived by the consumer as he/she
holds a particular product, rubs it across his/her skin, or crumples it within
his/her hand. This tactile sensation is provided by a combination of several
physical properties. One of the most important physical properties related to
softness is generally considered by those skilled in the art to be the
stiffness
of the paper web from which the product is made. Stiffness, in turn, is
usually considered to be directly dependent on the strength of the web.
Strength is the ability of the product, and its constituent webs, to
maintain physical integrity and to resist tearing, bursting, and shredding
under use conditions.
Linting and dusting refers to the tendency of a web to release
unbound or loosely bound fibers or particulate fillers during handling or use.
Creped tissue papers are generally comprised essentially of
papermaking fibers. Small amounts of chemical functional agents such as
wet strength or dry strength binders, retention aids, surfactants, size,
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chemical softeners, crepe facilitating compositions are frequently included
but these are typically only used in minor amounts. The papermaking fibers
most frequently used in creped tissue papers are virgin chemical wood
pulps.
As the world's supply of natural resources comes under increasing
economic and environmental scrutiny, pressure is mounting to reduce
consumption of forest products such as virgin chemical wood pulps in
products such as sanitary tissues. One way to extend a given supply of
wood pulp without sacrificing product mass is to replace virgin chemical
pulp fibers with high yield fibers such as mechanical or chemi-mechanical
pulps or to use fibers which have been recycled. Unfortunately,
comparatively severe deterioration in performance usually accompanies such
changes. Such fibers are prone to have a high coarseness and this
contributes to the loss of the velvety feel which is imparted by prime fibers
selected because of their flaccidness. In the case of the mechanical or
chemi-mechanical liberated fiber, high coarseness is due to the retention of
the non-cellulosic components of the original wood substance, such
components including lignin and so-called hemiceliuloses. This makes each
fiber weigh more without increasing its length. Recycled paper can also
tend to have a high mechanical pulp content, but, even when all due care is
exercised in selecting the wastepaper grade to minimize this, a high
coarseness still often occurs. This is thought to be due to the impure
mixture of fiber morphologies which naturally occurs when paper from many
sources is blended to make a recycled pulp. For example, a certain
wastepaper might be selected because it is primarily North American
hardwood in nature: however, one will often find extensive contamination
from coarser softwood fibers, even of the most deleterious species such as
variations of Southern U.S. pine. U.S. Patent 4,300,98'x, Carstens, issued
November 17, 1981, explains the textural and surface qualities which are
imparted by prime fibers. U.S. Patent No 5,228,954, Vinson, issued July 20,
1993, and U.S. Patent 5,405,499, Vinson, to issue April 11, 1995, disclose
methods for upgrading such fiber sources so that they have less deleterious
effects, but still the level of replacement is limited and
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the new fiber sources themselves are in limited supply and this often limits
their use.
Applicants have discovered that another method of limiting the use of ,
wood pulp in sanitary tissue paper is to replace part of it with a lower cost,
readily available filling material such as kaolin clay or calcium carbonate.
While those skilled in the art will recognize that this practice has been
common in some parts of the paper industry for many years, they will also
appreciate that extending this approach to sanitary tissue products has
involved particular difficulties which have prevented it from being practiced
up to now.
One major restriction is the retention of the filling agent during the
papermaking process. Among paper products, sanitary tissues are at an
extreme of low basis weight. The basis weight of a tissue web as it is
wound on a reel from a Yankee machine is typically only about 15 g/m2 and
because of the crepe, or foreshortening, introduced at the creping blade, the
dry fiber basis weight in the forming, press, and drying sections of the
machine is actually lower than the finished dry basis weight by from about
10% to about 20°~. To compound the difficulties in retention caused by
the
low basis weight, tissue webs occupy an extreme of low density, often
having an apparent density as wound on the reel of only about 0.1 g/cm3 or
less. While it is recognized that some of this loft is introduced at the
creping blade, those skilled in the art will recognize that tissue webs are
generally formed from relatively free stock which means that the fibers of
which they are comprised are not rendered flaccid from beating. Tissue
machines are required to operate at very high speeds to be practical; thus
free stock is needed to prevent excessive forming pressures and drying load.
The relatively stiff fibers comprising the free stock retain their ability to
prop
open the embryonic web as it is forming. Those skilled in the art will at
once recognize that such light weight, low density structures do not afford _
any significant opportunity to filter fine particulates as the web is forming.
Filler particles not substantively affixed to fiber surfaces will be torn away
by the torrent of the high speed approach flow systems, hurled into the
liquid phase, and driven through the embryonic web into the water drained
from the forming web. Only with repeated recycling of the water used to
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form the web does the concentration of particulate build to a point where
the filler begins to exit with the paper. Such concentrations of solids in
water effluent are impractical.
A second major limitation is the general failure of particulate fillers to
naturally bond to papermaking fibers in the fashion that papermaking fibers
tend to bond to each other as the formed web is dried. This reduces the
strength of the product. Filter inclusion causes a reduction in strength,
which if left uncorrected, severely limits products which are already quite
weak. Steps required to restore strength such as increased fiber beating or
the use of chemical strengthening agents is often restricted as well.
The deleterious effects of filler on sheet integrity also often cause
hygiene problems by plugging press felts or by transferring poorly from the
press section to the Yankee dryer.
Finally, tissue products containing fillers are prone to lint or dust.
This is not only because the fillers themselves can be poorly trapped within
the web, but also because they have the aforementioned bond inhibiting
effect which causes a localized weakening of fiber anchoring into the
structure. This tendency can cause operational difficulties in the creped
papermaking processes and in subsequent converting operations, because of
excessive dust created when the paper is handled. Another consideration is
that the users of the sanitary tissue products made from the filled tissue
demand that they be relatively free of lint and dust. Attempts to overcome
this tendency to lint or dust by using chemical binders or mechanical refining
invariably cause the tissue product to become harsh.
Consequently, the use of fillers in papers made on 'Yankee machines
has been severely limited. United States Patent 2,216,1413, issued to Thiele
on October 1, 1940, discusses the limitations of fillers on Yankee machines
and discloses a method of incorporation which overcomes those limitations.
Unfortunately, the method requires a cumbersome unit operation to coat a
layer of adhesively bound particles onto the felt side of the sheet while it
is in
contact with the Yankee dryer. This operation is not practical for modern high
speed Yankee machines and, those skilled in the art will recognize that the
Thiele method
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would produce a coated rather than filled tissue product. A "filled tissue
paper" is distinguished from "coated tissue paper" essentially by the
methods practiced to produce them, i.e. a "filled tissue paper" is one which
has the particulate matter added to the fibers prior to their assembly into a
web while a "coated tissue paper" is one which has the particulate matter
added after the web has been essentially assembled. As a result of this
difference, a filled tissue paper product can be described as a relatively
lightweight, low density creped tissue paper made on a 'Yankee machine
which contains a filler dispersed throughout the thickness of at least one
layer of a multi-layer tissue paper, or throughout the entire thickness of a
single-layered tissue paper. The term "dispersed throughout" means that
essentially all portions of a particular layer of a filled tissue product
contain
filler particles, but, it specifically does not imply that such dispersion
necessarily be uniform in that layer. In fact, certain advantages can be
anticipated by achieving a difference in filler concentration as a function of
thickness in a filled layer of tissue.
Therefore, it is the object of an aspect of the present invention to
provide for a tissue paper comprising a fine particulate filler which
overcomes
the aforementioned limitations of the prior art. The tissue paper of the
present
invention is soft, contains a retentive filler, has a high level of tensile
strength,
and is low in dust.
This and other objects are obtained using the present invention as will
be taught in the following disclosure.
SUMMA Y OF THE~I~VENTI N
In an aspect of the present invention, there is provided a strong, soft
filled tissue paper, low in lint and dust, and having biased surface bonding
characterisitcs. The filled tissue paper with biased surface bonding comprises
papermaking fibers and a non-cellulosic particulate filler, said filler
preferably
comprising from about 15% to about 50% by weight of said tissue. The
surface properties of the tissue product are biased to a degree that the lint
ratio is at least about 1.2, and more preferably at least about 1.4.
Unexpected
combinations of softness,
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strength, and resistance to dusting have been obtained by filling creped
tissue paper with biased surface properties with these levels of particulate
fillers.
In its preferred embodiment, the filled tissue paper of the present
invention has a basis weight between about 10 g/m2 and about 50 g/m2
and, more preferably, between about 10 g/m2 and about 30 g/m2. It has a
density between about 0.03 g/m3 and about 0.6 g/m3 and, more preferably,
between about 0.05 g/m3 and 0.2 g/m3.
The preferred embodiment further comprises papermaking fibers of
both hardwood and softwood types wherein at least about 50% of the
papermaking fibers are hardwood and at least about 10% are softwood.
The hardwood and softwood fibers are most preferably isolated by providing
separate layers wherein the fraction of softwood fibers relative to hardwood
fibers differ by different layers. Preferably, the tissue comprises an inner
layer and two outer layers wherein the inner layer fiber content is
predominantly softwood and the outer layer fiber content is predominately
hardwood.
The preferred tissue paper of the present invention is pattern densified
such that zones of relatively high density are dispersed within a high bulk
field, including pattern densified tissue wherein zones of relatively high
density are continuous and the high bulk field is discrete. Most preferably,
the tissue paper is through air dried.
The invention provides for a creped tissue paper comprising
papermaking fibers and a particulate filler. In its preferred embodiment, the
particulate filler is selected from the group consisting of clay, calcium
carbonate, titanium dioxide, talc, aluminum silicate, calcium silicate,
alumina
trihydrate, activated carbon, pearl starch, calcium sulfate, glass
microspheres, diatomaceous earth, and mixtures thereof. When selecting a
filler from the above group several factors need to be evaluated. These
include cost, availability, ease of retaining into the tissue paper, color,
scattering potential, refractive index, and chemical compatibility with the
selected papermaking environment.
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g
A particularly suitable filler is kaolin clay. Most preferably the so called
"hydrous aluminum silicate" form of kaolin clay is preferred as contrasted to
the kaolins which are further processed by calcining.
The preferred embodiment of the present invention employs a bond
inhibiting agent. Preferred bond inhibiting agents comprise the well known
dialkyldimethylammonium salts such as ditallowdimethylammonium, chloride,
ditallowdimethylammonium methyl sulfate, di(hydrogenated) tallow dimethyl
ammonium chloride; with di(hydrogenated) tallow dimethyl ammonium methyl
sulfate being particularly preferred. In its most preferred form, the present
invention employs the bond inhibiting agent preferentially biased toward the
Yankee-side surface.
The morphology of kaolin is naturally platy or blocky, but it is preferable
to use clays which have not been subjected to mechanical delamination
treatments as this tends to reduce the mean particle size. It is common to
refer to the mean particle size in teems of equivalent spherical diameter. An
average equivalent spherical diameter greater than about 0.2 micron, more
preferably greater than about 0.5 micron is preferred in the practice of the
present invention. Most preferably, an equivalent spherical diameter greater
than about 1.0 micron is preferred.
In accordance with another aspect of the present invention, there is
provided a strong, soft and low dusting filled, layered creped tissue paper
characterized in that it comprises papermaking fibers and a non-cellulosic
particulate filler, said tissue paper having biased surface bonding properties
such that the lint ratio is at least 1.2, more preferably the lint ratio is at
least
1.4.
All percentages, ratios and proportions herein are by weight unless
otherwise specified.
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8a
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation illustrating a creped
papermaking process of the present invention for producing a strong, soft,
and low lint creped tissue paper comprising papermaking fibers and
particulate fillers.
Figure 2 is a schematic representation illustrating the steps for
preparing the aqueous papermaking furnish for the creped papermaking
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process, according to one embodiment of the present invention based on
cationic flocculant.
Figure 3 is a schematic representation illustrating the steps for
preparing the aqueous papermaking furnish for the creped papermaking
process, according to another embodiment of the present invention based on
anionic flocculant.
Figure 4 is a cross-sectional view illustrating a three-layered single-ply
creped tissue paper according to the present invention.
NAILED DESCRIPTION OF THE INVENTION
While this specification concludes with claims particularly pointing out
and distinctly claiming the subject matter regarded as the invention, it is
believed that the invention can be better understood from a reading of the
following detailed description and of the appended examples.
As used herein, the term "comprising" means that the various
components, ingredients, or steps, can be conjointly employed in practicing
the present invention. Accordingly, the term "comprising" encompasses the
more restrictive terms "consisting essentially of" and "consisting of."
As used herein, the term "predominantly" means more than one-half
by weight.
As used herein, the term "water soluble" refers to materials that are
soluble in water to at least 3%, by weight, at 25 °C.
As used herein, the terms "tissue paper web, paper web, web, paper
sheet and paper product°' all refer to sheets of paper made by a
process
comprising the steps of forming an aqueous papermaking furnish, depositing
this furnish on a foraminous surface, such as a Fourdrinier wire, and
removing the water from the furnish as by gravity or vacuum-assisted
drainage, with or without pressing, and by evaporation, comprising the final
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steps of adhering the sheet in a semi-dry condition to the surface of a
Yankee dryer, completing the water removal by evaporation to an essentially
dry state, removal of the web from the Yankee dryer by means of a flexible
creping blade, and winding the resultant sheet onto a reel.
As used herein, the term °'filled tissue paper" means a paper
product
that can be described as a relatively lightweight, low density creped tissue
paper made on a Yankee machine which contains a filler dispersed
throughout the thickness of at least one layer of a mufti-layer tissue paper.
The term "dispersed throughout" means that essentially all portions of a
particular layer of a filled tissue product contain filler particles, but, it
specifically does not imply that such dispersion necessarily be uniform in
that layer. In fact, certain advantages can be anticipated by achieving a
difference in filler concentration as a function of thickness in a filled
layer of
tissue.
The terms "mufti-layered tissue paper web, mufti-layered paper web,
mufti-layered web, mufti-layered paper sheet and mufti-layered paper
product" are all used interchangeably in the art to refer to sheets of paper
prepared from two or more layers of aqueous paper making furnish which
are preferably comprised of different fiber types, the fibers typically being
relatively long softwood and relatively short hardwood fibers as used in
tissue paper making. The layers are preferably formed from the deposition of
separate streams of dilute fiber slurries upon one or more endless
foraminous surfaces. If the individual layers are initially formed on separate
foraminous surfaces, the layers can be subsequently combined when wet to
form a mufti-layered tissue paper web.
As used herein, the term "single-ply tissue product" means that it is
comprised of one ply of creped tissue; the ply can be substantially
homogeneous in nature or it can be a mufti-layered tissue paper web. As
used herein, the term "mufti-ply tissue product" means that it is comprised
of more than one ply of creped tissue. The plies of a mufti-ply tissue product
can be substantially homogeneous in nature or they can be mufti-layered
tissue paper webs.
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The first step in the process of this invention is the forming of at least
one "aqueous papermaking furnish", a term which, as used herein, refers to
a suspension of papermaking fibers, usually comprised of wood pulp, and
particulate fillers, along with the additives which are essential to provide
the
retention of the particulate filler and any other functional properties by
optionally including modifying chemicals as described hereinafter. Some
typical components of the papermaking furnish are described in the
following section.
Ingredients of the Papermaking I=urnish
The Pai~ermaking Fibers
It is anticipated that wood pulp in all its varieties will normally
comprise the papermaking fibers used in this invention. However, other
cellulose fibrous pulps, such as cotton linters, bagasse, rayon, etc., can be
used and none are disclaimed. Wood pulps useful herein include chemical
pulps such as sulfite and sulfate (sometimes called Kraft) pulps as well as
mechanical pulps including for example, ground wood, ThermoMechanical
Pulp (TMP) and Chemi-ThermoMechanical Pulp (CTMP). Pulps derived from
both deciduous and coniferous trees can be used.
Both hardwood pulps and softwood pulps as well as combinations of
the two may be employed as papermaking fibers for the tissue paper of the
present invention. The term "hardwood pulps" as used herein refers to
fibrous pulp derived from the woody substance of deciduous trees
(angiosperms), whereas "softwood pulps" are fibrous pulps derived from the
woody substance of coniferous trees (gymnosperms). Blends of hardwood
Kraft pulps, especially eucalyptus, and northern softwood Kraft (NSK) pulps
are particularly suitable for making the tissue webs of the present invention.
A preferred embodiment of the present invention comprises layered tissue
webs wherein, most preferably, hardwood pulps such as eucalyptus are
used for outer layers) and wherein northern softwood Kraft pulps are used
for the inner layer(s). Also applicable to the present invention are fibers
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derived from recycled paper, which may contain any or all of the above
categories of fibers.
The Particulate Filler
The invention provides for a creped tissue paper comprising
papermaking fibers and a particulate filler. In its preferred embodiment, the
particulate filler is selected from the group consisting of clay, calcium
carbonate, titanium dioxide, talc, aluminum silicate, calcium silicate,
alumina
trihydrate, activated carbon, pearl starch, calcium sulfate, glass
microspheres, diatomaceous earth, and mixtures thereof. When selecting a
filler from the above group several factors need to be evaluated. These
include cost, availability, ease of retaining into the tissue paper, color,
scattering potential, refractive index, and chemical compatibility with the
selected papermaking environment.
It has now been found that a particularly suitable particulate filler is
kaolin clay. Kaolin clay is the common name for a class of naturally
occurring aluminum silicate mineral beneficiated as a particulate.
With respect to terminology, it is noted that it is common in the
industry, as well as in the prior art patent literature, when referring to
kaolin
products or processing, to use the term "hydrous" to refer to kaolin which
has not been subject to calcination. Calcination subjects the clay to
temperatures above 450oC, which temperatures serve to alter the basic
crystal structure of kaolin. The so-called "hydrous" kaolins may have been
produced from crude kaolins, which have been subjected to beneficiation,
as, for example, to froth flotation, to magnetic separation, to mechanical
delamination, grinding, or similar comminution, but not to the mentioned
heating as would impair the crystal structure.
To be accurate in a technical sense, the description of these materials
as "hydrous" is inappropriate. More specifically, there is no molecular water
actually present in the kaolinite structure. Thus although the composition
can be, and often is, arbitrarily written in the form ZH20oA1203o2Si02, it
has long been known that kaolinite is an aluminum hydroxide silicate of
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approximate composition A12(OH)4Si205, which equates to the hydrated
formula just cited. Once kaolin is subjected to calcination, which for the
purposes of this specification refers to subjecting a kaolin to temperatures
- exceeding 450oC, for a period sufficient to eliminate the hydroxyl groups,
the original crystalline structure of the kaolinite is destroyed. Therefore,
although technically such calcined clays are no longer "kaolin", it is common
in the industry to refer to these as calcined kaolin, and, for the purposes of
this specification, the calcined materials are included when the class of
materials "kaolin" is cited. Accordingly, the term "hydrous aluminum
silicate" refers to natural kaolin, which has not been subjected to
calcination.
Hydrous aluminum silicate is the kaolin form most preferred in the
practice of the present invention. It is therefore characterized by the before
mentioned approximate 13% by weight loss as water vapor at temperatures
exceeding 450oC.
The morphology of kaolin is naturally platy or blocky, because it
naturally occurs in the form of thin platelets which adhere together to form
"stacks'° or "books". The stacks separate to some degree into the
individual
platelets during processing, but it is preferable to use clays which have not
been subjected to extensive mechanical delamination treatments as this
tends to reduce the mean particle size. It is common to refer to the mean
particle size in terms of equivalent spherical diameter. An average
equivalent spherical diameter greater than about 0.2 micron, more preferably
greater than about 0.5 micron is preferred in the practice of the present
invention. Most preferably, an equivalent spherical diameter greater than
about 1.0 micron is preferred.
Most mined clay is subjected to wet processing. Aqueous suspending
of the crude clay allows the coarse impurities to be removed by
centrifugation and provides a media for chemical bleaching. A polyacrylate
polymer or phosphate salt is sometimes added to such slurries to reduce
viscosity and slow settling. Resultant clays are normally shipped without
drying at about 70% solids suspensions, or they can be spray dried.
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Treatments to the clay, such as air floating, froth flotation, washing,
bleaching, spray drying, the addition of agents as slurry stabilizers and
viscosity modifiers, are generally acceptable and should be selected based
upon the specific commercial considerations at hand in a particular -
circumstance.
Each clay platelet is itself a multi-layered structure of aluminum
polysilicates. A continuous array of oxygen atoms forms one face of each
basic layer. The polysilicate sheet structure edges are united by these
oxygen atoms. A continuous array of hydroxyl groups of joined octahedral
alumina structures forms the other face forming a two-dimensional
polyaluminum oxide structure. The oxygen atoms sharing the tetrahedral
and octahedral structures bind the aluminum atoms to the silicon atoms.
Imperfections in the assembly are primarily responsible for the natural
clay particles possessing an anionic charge in suspension. This happens
because other di-, tri-, and tetra-valent cations substitute for aluminum. The
consequence is that some of the oxygen atoms on the surface become
anionic and become weakly dissociable hydroxyl groups.
Natural clay also has a cationic character capable of exchanging their
anions for others that are preferred. This happens because aluminum atoms
lacking a full complement of bonds occur at some frequency around the
peripheral edge of the platelet. They must satisfy their remaining valencies
by attracting anions from the aqueous suspension that they occupy. If
these cationic sites are not satisfied with anions from solutions, the clay
can
satisfy its own charge balance by orienting itself edge to face assembling a
°card house" structure which forms thick dispersions. Polyacrylate
dispersants ion exchange with the cationic sites providing a repulsive
character to the clay preventing these assemblies and simplifying the
production, shipping, and use of the clay.
A kaolin grade WW Fil SD~ is a spray dried kaolin marketed by Dry
Branch Kaolin Company of Dry Branch, Georgia suitable to make creped
tissue paper webs of the present invention.
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rch
In some aspects of the invention, it is useful to include starch as one
of the ingredients of the papermaking furnish. A starch that has limited
solubility in water in the presence of particulate fillers and fibers is
particularly useful in certain aspects of the invention to be detailed later.
A
common means of achieving this is to use a so called "cationic starch".
As used herein the term "cationic starch'° is defined as starch, as
naturally derived, which has been further chemically modified to impart a
cationic constituent moiety. Preferably the starch is derived from corn or
' potatoes, but can be derived from other sources such as rice, wheat, or
tapioca. Starch from waxy maize also known industrially as amioca starch is
particularly preferred. Amioca starch differs from common dent corn starch
in that it is entirely amylopectin, whereas common corn starch contains both
amylopectin and amylose. Various unique characteristics of amioca starch
are further described in "Amioca - The Starch from Waxy Corn", H. H.
Schopmeyer, Food Industries, December 1945, pp. 106-108. The starch can
be in granular form, pre-gelatinized granular form, or dispersed form. The
dispersed form is preferred. If in granular pre-gelatinized form, it need only
be dispersed in cold water prior to its use, with the only pre-caution being
to
use equipment which overcomes any tendency to gel-block in forming the
dispersion. Suitable dispersers known as eductors are common in the
industry. If the starch is in granular form and has not been pre-gelatinized,
it
is necessary to cook the starch to induce swelling of the granules.
Preferably, such starch granules are swollen, as by cooking, to a point just
prior to dispersion of the starch granule. Such highly swollen starch granules
shall be referred to as being "fully cooked". The conditions for dispersion in
general can vary depending upon the size of the starch granules, the degree
of crystallinity of the granules, and the amount of amylose present. Fully
cooked amioca starch, for example, can be prepared by heating an aqueous
slurry of about 4% consistency of starch granules at about 190 °F
(about
88 °C) for between about 30 and about 40 minutes.
Cationic starches can be divided into the following general
classifications: (1 ) tertiary aminoalkyl ethers, (2) opium starch ethers
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including quaternary amines, phosphonium, and sulfonium derivatives, (3)
primary and secondary aminoalkyl starches, and (4) miscellaneous (e.g.,
imino starches). New cationic products continue to be developed, but the
tertiary aminoalkyl ethers and quaternary ammonium alkyl ethers are the main
commercial types. Preferably, the cationic starch has a degree of substitution
ranging from about 0.01 to about 0.1 cationic substituent per anhydroglucose
units of starch; the substituents preferably chosen from the above mentioned
types. Suitable starches are produced by National Starch and Chemical
Company, (Bridgewater, New Jersey) under the RediBONDT"", Grades with
cationic moieties only such as RediBOND 5320 T"" and RediBOND 5327T"~ are
suitable, and grades with additional anionic functionality such as RediBOND
2005T"" are also suitable.
While not wishing to be bound by theory, it is believed that the
cationic starch which is initially dissolved in water, becomes insoluble in
the
presence of filler because of its attraction for the anionic sites on the
filler
surface. This causes the filler to be covered with the bushy starch
molecules which provide an attractive surface for more filter panicles,
ultimately resulting in agglomeration of the filler. The essential element of
this step is believed to be the size and shape of the starch molecule rather
than the charge characteristics of the starch. For example, inferior results
would be expected by substituting a charge biasing species such as
synthetic linear polyelectrolyte for the cationic starch.
in one embodiment of the present invention, cationic starch is
preferably added to the particulate filler. In this case, the amount of
cationic
starch added is from about 0.196 to about 2%, but most preferably from
about 0.25% to about 0.75%, by weight based on the weight of the
particulate fitter. In this aspect of the invention, it is preferable to use a
cationic flocculant as a retention aid.
In another embodiment of the present invention, it is preferred to add
cationic starch to an entire a4ueous papermaking furnish, preferably at a
point before the final dilution at the fan pump. This aspect of the invention
makes use of an anionic flocculant as a retention aid. In this aspect of the
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17
invention, it is preferable to add cationic starch at a rate from about five
to
about twenty times the rate of the anionic flocculant.
The cationic and anionic floccutants mentioned in the above are
described in detail in the following sections.
A number of materials are marketed as so-called retention aids", a
term as used herein, referring to additives used to increase the retention of
the fine furnish solids in the web during the papermaking process. Without
adequate retention of the fine solids, they are either lost to the process
effluent or accumulate to excessively high concentrations in the recircuiating
white water loop and cause production difficulties including deposit build-up
and impaired drainage. Chapter 17 entitled "Retention Chemistry" of "Pulp
and Paper, Chemistry and Chemical Technology", 3rd ed. Vol. 3, by J. E.
Unbehend and K. W. Britt, A Wiley Interscience Publication, provides the
essential understanding of the types and mechanisms by which polymeric
retention aids function. A flocculant agglomerates suspended particles
generally by a bridging mechanism. While certain multivalent cations are
considered common flocculants, they are generally being replaced in practice
by superior acting polymers which carry many charge sites along the polymer
chain.
Tissue products according to the present invention can be effectively
produced using as a retention aid a cationic flocculant", a term which, as
used herein, refers to a class of poiyelectrolyte. These polymers generally
originate from copolymeriZation of one or more ethylenically unsaturated
monomers, generally acrylic monomers, that consist of or include cationic
monomer.
Suitable cationic monomers are dialkyl amino alkyl-(meth) acrylates or
-(meth) acrylamides, either as acid salts or quaternary ammonium salts.
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18
Suitable alkyl groups include dialkylaminoethyl (meth) acrylates,
dialkylaminoethyl (meth) acrylamides and dialkylaminomethyl (meth)
acrylamides and diatkylamino -1,3-propyl (meth) acrylamides. These cationic
monomers are preferably copolymerized with a nonionic monomer,
preferably acryfamide. Other suitable polymers are polyethylene imines,
polyamide epichlorohydrin polymers, and homopolymers or copolymers,
generally with acrylamide, of monomers such as diatlyl dimethyl ammonium
chloride.
Any conventional cationic synthetic polymeric flocculant suitable for
use on paper as a retention aid can be usefully employed to make products
according to the present invention.
The polymer is preferably substantially linear in comparison to the
globular structure of cationized starches.
A wide range of charge densities is useful, although a medium density
is preferred. Polymers useful to make products of the present invention
contain cationic functional groups at a frequency ranging from as low as
about 0.2 to as high as 2.5, but more preferably in a range of about 1 to
about 1.5 milliequivalents per gram of polymer.
Polymers useful to make tissue products according to the present
invention should have a molecular weight of at least about 500,000, and
preferably a molecular weight above about 1,000,000, and, may
advantageously have a molecular weight above 5,000,000.
Examples of acceptable materials are RETEN 1232° and Microform
2321~, both emulsion polymerized cationic polyacrytamides and RETEN
157~, which is delivered as a solid granule; all are products of Hercules,
Inc.
of Wilmington, Delaware. Another acceptable cationic flocculant is Accurac
91, a product of Cytec, Inc. of Stamford, CT.
Those skilled in the art will recognize that the desired usage rates of
these polymers will vary widely. Amounts as low as about 0.005% polymer
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19
by weight based on the dry weight of the polymer and the dry finished
weight of tissue paper will deliver useful results, but normally the usage
rate
would be expected to be higher; even higher for the purposes of the present
invention than commonly practiced as application of these materials.
Amounts as high as about 0.5% might be employed, but normally about
0.1 % is optimum.
Anionic Flocculant
In another aspect of the present invention, an "anionic flocculant" is
an useful ingredient. An "anionic flocculant" as used herein refers to a high
molecular weight polymer having pendant anionic groups.
Anionic polymers often have a carboxylic acid (-COOH) moiety.
These can be immediately pendant to the polymer backbone or pendant
through typically, an alkalene group, particularly an alkalene group of a few
carbons. In aqueous medium, except at low pH, such carboxylic acid
groups ionize to provide to the polymer a negative charge.
Anionic polymers suitable for anionic flocculants do not wholly or
essentially consist of monomeric units prone to yield a carboxylic acid group
upon polymerization, instead they are comprised of a combination of
monomers yielding both nonionic and anionic functionality. Monomers
yielding nonionic functionality, especially if possessing a polar character,
often exhibit the same flocculating tendencies as ionic functionality. The
incorporation of such monomers is often practiced for this reason. An often
used nonionic unit is (meth) acrylamide.
Anionic polyacrylamides having relatively high molecular weights are
satisfactory flocculating agents. Such anionic polyacrylamides contain a
combination of (meth) acrylamide and (meth) acrylic acid, the latter of which
can be derived from the incorporation of (meth)acrylic acid monomer during
the polymerization step or by the hydrolysis of some (meth) acrylamide units
after the polymerization, or combined methods.
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?0
The polymer is preferably substantially linear in comparison to the
globular structure of anionic starch.
A wide range of charge densities is useful, although a medium density
is preferred. Polymers useful to make products of the present invention
contain cationic functional groups at a frequency ranging from as low as
about 0.2 to as high as about 7 or higher, but more preferably in a range of
about Z to about 4 milliequivalents pet gram of polymer.
Polymers useful to make tissue products according to the present
invention should have a molecular weight of at least about 500,000. and
preferably a molecular weight above about 7 ,000,000, and, may
advantageously have a molecular weight above 5,000,000.
An example of an acceptable material is RETEN 235T"", which is
delivered as a solid granule; a product of Hercules, Inc. of Wilmington,
Delaware. Another acceptable anionic flocculant is Accurac 62T"", a product
of Cytec, Inc. of Stamford, CT.
Those skilled in the art will recognize that the desired usage rates of
these polymers will vary widely. Amounts as low as about 0.005 % polymer
by weight based on the finished dry weight of tissue paper will deliver useful
results, but normally the usage rate would be expected to be higher; even
higher for the purposes of the present invention than commonly practiced as
application of these materials. Amounts as high as about 0.5 °~ might
be
empioyad, but normally about 0.1 ~6 is optimum.
Bond inhibiting agents are expressly included in the present invention.
Acceptable bond inhibiting agents comprise the welt known
dialkyldirnethylammonium salts such as ditalfowdimethylammonium chloride,
ditallowdimethyiammonium methyl sulfate, dilhydrogenatedl tallow dimethyl
ammonium chloride; with dilhydrogenated) tallow dimethyl ammonium
methyl sulfate being preferred. This particular material is available
commercially from Witco Chemical Company Inc. of Dublin, Ohio under the
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21
Varisoft 137T"". Bond inhibiting agents act to disrupt the natural
fiber to fiber bonding that occurs during the papermaking process. The
level of bond inhibiting agent, if used, is preferably from about 0.02% to
about 0.5 %, by weight based on the dry weight of the tissue paper. Most
preferably, the bond inhibiting agent is used in the Yankee side layer.
OthP,~ Additives
Other materials can be added to the aqueous papermaking furnish or
the embryonic web to impart other characteristics to the product or improve
the papermaking process so long as they are compatible with the chemistry
of the selected particulate filler and do not significantly and adversely
affect
the softness, strength, or low dusting character of the present invention.
The following materials are expressly included, but their inclusion is not
offered to be all-inclusive. Other materials can be included as well so long
as they do not interfere or counteract the advantages of the present
invention.
It is common to add a cationic charge biasing species to the
papermaking process to control the zeta potential of the aqueous
papermaking furnish as it is delivered to the papermaking process. These
materials are used because rrrost of the solids in nature have negative
surface charges, including the surfaces of ceilulosic fibers and fines and
most inorganic fillers, Many experts in the field believe that a cationic
charge biasing species is desirable as it partially neutralizes these solids.
making them more easily flocculated by cationic flocculants such as the
before mentioned cationic starch and cationic polyeiectrolyte. One
traditionally used cationic charge biasing species is alum. More recently in
the art, charge biasing is done by use of relatively low molecular weight
cationic synthetic polymers preferably having a molecular weight of no more
than about 500.000 and more preferably no more than about 200,000, or
even about 100.000. The charge densities of such low molecular weight
cationic synthetic polymers are relatively high. These charge densities range
polymer. One suitable material is Cypro 514T"~, a product of Cytec, Inc. of
Stamford. CT. The use of sucin materials is expr~asly allowed ~Nithin the
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practice of the present invention. Caution should be used in their
application, however. It is well known that while a small amount of such
agents can actually aid retention by neutralizing anionic centers inaccessible
to the larger fiocculant molecules and thereby towering the particle
repulsion; however, since such materials can compete with cationic
flocculants for anionic anchoring sites, they can actually have an effect
opposite to the intended one by negatively impacting retention when anionic
sites are limited.
The use of high surface area, high anionic charge microparticles for the
purposes of improving formation, drainage, strength, and retention is well
taught in the art. See, for example, U. S. 'Patent, 5,22'1,435, issued to
Smith on June 22, 1993. Common materials for this purpose are silica colloid,
or bentonite clay. The incorporation of such materials is expressly included
within the scope of the present invention.
if permanent wet strength is desired, the group of chemicals: including
poiyamide-epichlorohydrin, polyacrylamides, styrene-butadiene lances;
insolubiiized polyvinyl alcohol; urea-formaldehyde; polyethyieneimine;
chitosan polymers and mixtures thereof can be added to the papermaking
furnish or to the embryonic web. Polyamide-epichlorohydrin resins are
cationic wet strength resins which have been found to be of particular
utility. Suitable types of such resins are described in U.S. Patent No.
3,700.fi23. issued on October 24. 1972, and 3.772.076, issued on
November 13, 1973, both issued to Keim. One commercial source of a useful
polyamide-epichlorohydrin resins is Hercules, inc. of Wilmington, Delaware,
which markets such resin under the mark Kymene 557HT"'.
Many creped paper products must have limited strength when wet
because of the need to dispose of them through toilets into septic or sewer
systems. If wet strength is imparted to these products, it is preferred to be
fugitive wet strength characterized by a decay of part or all of its potency
upon standing in presence of water. If fugitive wet strength is desired, the
CA 02236571 2002-07-23
23
binder materials can be chosen from the group consisting of dialdehyde starch
or
other resins with aldehyde functionality such as Co-Bond 1000 T"' offered by
National Starch and Chemical Company, Parez 750T"" offered by Cytec of
Stamford, CT and the resin described in U.S. Patent No. 4,981,557 issued on
January 1, 1991, to Bjorkquist.
If enhanced absorbency is needed, surfactants may be used to treat the
creped tissue paper webs of the present invention. 'The level of surfactant,
if
used, is preferably from about 0.01 % to about 2.0% by weight, based on the
dry
fiber weight of the tissue paper. The surfactants preferably have alkyl chains
with
eight or more carbon atoms. Exemplary anionic surfactants are linear alkyl
sulfonates, and alkylbenzene sulfonates. Exemplary nonionic: surfactants are
alkylglycosides including alkylglycoside esters such as Crodesta SL-40T""
which
is available from Croda, Inc. (New York, NY); alkylgiycoside ethers as
described
in U.S. Patent 4,011,389, issued to W. K. Langdon, et al. on March 8, 1977;
and
alkylpolyethoxylated esters such as Pegosperse 2U0 MLT"' available from Glyco
Chemicals, Inc. (Greenwich, CT) and IGEPAL RC-520T"' available from Rhone
Poulenc Corporation (Cranbury, NJ).
The present invention an also be used in conjunction with adhesives and
coatings designed to be sprayed onto the surface of the web or onto the Yankee
dryer, such products designed for controlling adhesion to the Yankee dryer.
For
example, U.S. Patent 3,926,716, Bates, discloses a process using an aqueous
dispersion of polyvinyl alcohol of certain degree of hydrolysis and viscosity
for
improving the adhesion of paper webs to Yankee dryers. Such polyvinyl
alcohols, sold under the tradename AirvoIT"" by Air Products and Chemicals,
Inc.
of Allentown, PA can be used in conjunction with the present invention. Other
Yankee coatings similarly recommended for use directly on the Yankee or on the
surface of the sheet are cationic polyamide or poiyamine resins such as
RezosolT"" and UnisoftT"' by Houghton International of Valley Forge, PA and
CrepetrolT"~ by Hercules, Inc. of Wilmington, Delaware. These can also be used
with the present
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24
invention. Preferably the web is secured to the Yankee dryer by means of
an adhesive selected from the group consisting of partially hydrolyzed
polyvinyl alcohol resin, polyamide resin, polyamine resin, mineral oil, and
mixtures thereof. More preferably, the adhesive is selected from the group
consisting of polyamide epichlorohydrin resin, mineral oil, and mixtures
thereof.
The above listings of optional chemical additives is intended to be
merely exemplary in nature, and are not meant to limit the scope of the
invention.
Preparation of the Aqueous Papermaking Furnish
Those skilled in the art will recognize that not only the qualitative
chemical composition of the papermaking furnish is important to the creped
papermaking process, but also the relative amounts of each component, and
the sequence and timing of addition, among other factors. It has now been
found that the following techniques are suitable in preparing the aqueous
papermaking furnish, but its delineation should not be regarded as limiting
the scope of the present invention, which is defined by the claims set forth
at the end of this specification.
Papermaking fibers are first prepared by liberating the individual fibers
into a aqueous slurry by any of the common pulping methods adequately
described in the prior art. Refining, if necessary, is then carried out on the
selected parts of the papermaking furnish. It has been found that there is an
advantage in retention, if the aqueous slurry which will later be used to
adsorb the particulate filler is refined at least to the equivalent of a
Canadian
Standard Freeness of about 600 ml, but, more preferably 550 ml or below.
Dilution generally favors the absorption of polymers and retention aids;
consequently, the slurry or slurries of papermaking fibers at this point in
the
preparation is preferably no more than from about 3-5% solids by weight.
The selected particulate filler is first prepared by also dispersing it into
an aqueous slurry. Dilution generally favors the absorption of polymers and
retention aids onto solids surfaces; consequently, the slurry or slurries of
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particulate filters at this point in the preparation is preferably no more
than
from about 1-5 % solids by weight.
One aspect of the invention is based on a cationic flocculant retention
chemistry. It involves first the addition of a starch with a limited water
solubility in the presence of the particulate filler. Preferably, the starch
is
cationic and it is added as an aqueous dispersion in an amount ranging from
about 0.3% by weight to 1.0% by weight, based on the dry weight of the
starch and the dry weight of the particulate filler, strictly to the dilute
aqueous slurry of particulate filler.
While not wishing to be bound by theory, it is believed that the starch
acts as an agglomerating agent onto the filler and results in agglomeration of
the particles. Agglomerating the filler in this manner makes it more
effectively adsorbed onto the surfaces of the papermaking fibers.
Adsorption of the filler onto the fiber surfaces can be accomplished by
combining the slurry of agglomerates with at least one slurry of papermaking
fibers and adding a cationic flocculant to the resultant mixture. Again, while
not wishing to be bound by theory, the action of the flocculant is thought to
be effective at this point by bridging between anionic sites on the
papermaking fibers and anionic sites on the filler agglomerates.
The cationic flocculant can be added at any suitable point in the
approach flow of the stock preparation system of the papermaking process.
It is particularly preferred to add the cationic flocculant after the fan pump
in
which the final dilution with the recycled machine water returned from the
process is made. It is well known in the papermaking field that shear stages
break down bridges formed by flocculating agents, and hence it is genera!
practice to add the flocculating agent after as many shear stages
encountered by the aqueous papermaking slurry as feasible.
A second aspect of the invention is based on an anionic flocculant. In
this aspect, the anionic flocculant is preferably added at least to an aqueous
slurry of the particulate filler while it is essentially isolated from the
remainder of the aqueous papermaking furnish. The combination of anionic
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26
flocculant and particulate filler is then combined with at least a portion of
the papermaking fibers and cationic starch is added to the mixture; this
combination and starch addition is preferably accomplished prior to the final
dilution of the process wherein the recycled machine water is combined with
the aqueous papermaking furnish and conveyed to a headbox by a fan
pump.
Advantageously, there is provided an additional dose of flocculant
after the starch is added. While it is essential in this aspect of the
invention
that the initial dose of flocculant be of the anionic type, the portion of
flocculant added after the fan pump can be of either the anionic type or
cationic type. Most preferably, this second dose of flocculant occurs after
the final dilution with the recycled machine water, i.e. after the fan pump.
It
is well known in the papermaking field that shear stages break down the
flocs formed by flocculating agents, and hence it is general practice to add
the flocculating agent after as many shear stages encountered by the
aqueous papermaking slurry as feasible.
Those skilled in the art will recognize that the before mentioned
recommended addition of flocculant directly to the particulate filler is an
exception to minimum shear stage approach; thus this aspect of the present
invention yields an unexpected advantage when at least a portion of the
anionic flocculant is added to the particulate filler while it is essentially
free
of the other components of the aqueous papermaking furnish and the
flocculant treated particulate filler is added to the papermaking fibers prior
to
the final dilution stage. A suitable ratio for point of addition of the
anionic
flocculant is about 4:1, i.e. for each 1 part of the total flocculant dosage
that is added after the fan pump, about 4 parts are advantageously added
directly to the particulate filler. This ratio can vary considerably, and it
is
anticipated that ratios from about 0.5:1 to 10:1 might be appropriate
depending on varying circumstances.
In preparing products representing either aspect of the invention, if
multiple slurries of papermaking fibers are prepared, one or more of the
slurries can be used to adsorb particulate fibers in accordance with the
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27
present invention. Even if one or more aqueous slurries of papermaking
fibers in the papermaking process is maintained relatively free of particulate
fillers prior to reaching its fan pump, it is preferred to add a cationic or
anionic flocculant after the fan pump of such slurries. This is because the
recycled water used in that fan pump contains filler agglomerates which
failed to retain in previous passes over the foraminous screen. When
multiple dilute fiber slurries are used in the creped papermaking process, the
flow of cationic or anionic flocculant is preferably added to all dilute fiber
slurries and it should be added in a manner which approximately proportions
it to the flow of solids in the aqueous papermaking furnish of each dilute
fiber slurry.
In a preferred arrangement, a slurry of relatively short papermaking
fibers, comprising hardwood pulp, is prepared and used to adsorb fine
particulate fillers, while a slurry of relatively long papermaking fibers,
comprising softwood pulp, is prepared and left essentially free of fine
particulates. The fate of the resultant short fibered slurry is to be directed
to the outer chambers of a three layered headbox to form surface layers of a
three layered tissue in which a long fibered inner layer is formed out of a
inner chamber in the headbox in which the slurry of relatively long
papermaking fibers is directed. The resultant filled tissue web is
particularly
suitable for converting into a single-ply tissue product.
In an alternate preferred arrangement, a slurry of relatively short
papermaking fibers, comprising hardwood pulp, is prepared and used to
adsorb fine particulate fillers, while a slurry of relatively long papermaking
fibers, comprising softwood pulp, is prepared and left essentially free of
fine
particulates. The fate of the resultant short fibered slurry is to be directed
to one chamber of a two chambered headbox to form one layer of a two
layered tissue in which a long fibered alternate layer is formed out of the
second chamber in the headbox in which the slurry of relatively long
papermaking fibers is directed. The resultant filled tissue web is
particularly
suitable for converting into a multi-ply tissue product comprising two plies
in
which each ply is oriented so that the layer comprised of relatively short
papermaking fibers is on the surface of the two-ply tissue product.
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In an alternate preferred arrangement, a slurry of relatively short
papermaking fibers, comprising hardwood pulp, is prepared and used to
adsorb fine particulate fibers, while a slurry of short papermaking fibers,
comprising hardwood pulp, is prepared and left relatively free of fine
particulates, and a slurry of relatively long papermaking fibers, comprising
softwood pulp, is prepared and left essentially free of fine particulates. The
fate of the resultant short fibered slurry containing fine particulate fillers
is to
be directed to one chamber of a multi-chambered headbox, while the
resultant short fibered slurry maintained relatively free of particulates is
directed to another chamber and the resultant long fibered slurry is directed
to a third chamber. Preferably the chambers are disposed such that the
chamber to which the relatively long fibered slurry is directed is disposed
between the other two chambers and the chamber carrying the relatively
short fibered slurry containing fine particulate fillers deposits its slurry
on the
opposite side of the foraminous surface.
Those skilled in the art will also recognize that the apparent number of
chambers of a headbox can be reduced by directing the same type of
aqueous papermaking furnish to adjacent chambers. For example, the
aforementioned three chambered headbox could be used as a two
chambered headbox simply by directing essentially the same aqueous
papermaking furnish to either of two adjacent chambers.
In all arrangements, it is essential to compose the furnish directed to
each layer to achieve the lint ratio prescribed by the present invention. This
is accomplished by preferentially adding starch to the furnish which is the
genesis of the off-Yankee side layer and thereby reducing the starch added
to the furnish which is the genesis of the Yankee-side layer. The lint ratio
is
also increased by adding a bond inhibiting agent preferentially into the
Yankee-side layer.
While not wishing to be bound by theory, it is believed that the
Yankee side surface of a filled tissue paper without biased surface properties
is less smooth than a similarly made tissue web which does not contain
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29
fillers. This is believed to arise from the necessity to bond the fibers more
tightly to overcome the strength loss associated with the displacement of
fibers with fine particulate. This difference is not noticeable on the off-
Yankee side, because this side naturally contains more surface variation.
Consequently, reducing the bonding on the wire side has a positive effect
which outweighs the negatives associated with further increasing the
bonding on the off-Yankee side layer.
Further insight into preparation methods for the aqueous papermaking
furnish can be gained by reference to Figure 2, which is a schematic
representation illustrating a preparation of the aqueous papermaking furnish
for the creped papermaking operation yielding a product according to the
aspect of the invention based on cationic flocculant and Figure 3, which is a
schematic representation illustrating a preparation of the aqueous
papermaking furnish for the creped papermaking operation yielding a
product according to another aspect of the invention based on anionic
flocculant. The following discussion refers to Figure 2:
A storage vessel 1 is provided for staging an aqueous slurry of
relatively long papermaking fibers. The slurry is conveyed by means of a
pump 2 and optionally through a refiner 3 to fully develop the strength
potential of the long papermaking fibers. Additive pipe 4 conveys a resin to
provide for wet or dry strength, as desired in the finished product. The
slurry is then further conditioned in mixer 5 to aid in absorption of the
resin.
The suitably conditioned slurry is then diluted with white water 7 in a fan
pump 6 forming a dilute long papermaking fiber slurry 15. Pipe 20 adds a
cationic flocculant to the slurry 15, producing a flocculated long fibered
slurry 22.
Still referring to Figure 2, a storage vessel 8 is a repository for a fine
particulate filler slurry. Additive pipe 9 conveys an aqueous dispersion of a
cationic starch additive. Pump 10 acts to convey the fine particulate slurry
as well as provide for dispersion of the starch. The slurry is conditioned in
a
mixer 12 to aid in absorption of the additives. Resultant slurry 13 is
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conveyed to a point where it is mixed with an aqueous dispersion of refined
short fiber papermaking fibers.
Still referring to Figure 2, short papermaking fiber slurry originates
from a repository 11, from which it is conveyed through pipe 49 by pump
14 through a refiner 15 where it becomes a refined slurry of short
papermaking fibers 16. After mixing with the conditioned slurry of fine
particulate filler 13, it becomes the short fiber based aqueous papermaking
slurry 17. White water 7 is mixed with slurry 17 in a fan pump 18 at which
point the slurry becomes a dilute aqueous papermaking slurry 19. Pipe 21
directs a cationic flocculant into slurry 19, after which the slurry becomes a
flocculated aqueous papermaking slurry 23.
Preferably, the flocculated short-fiber based aqueous papermaking
slurry 23 is directed to the creped papermaking process illustrated in Figure
1 and is divided into two approximately equal streams which are then
directed into headbox chambers 82 and 83 ultimately evolving into off-
Yankee-side-layer 75 and Yankee-side-layer 71, respectively of the strong,
soft, low dusting, filled creped tissue paper. Similarly, the aqueous
flocculated long papermaking fiber slurry 22, referring to Figure 2, is
preferably directed into headbox chamber 82b ultimately evolving into center
layer 73 of the strong, soft, low dusting, filled creped tissue paper.
The following discussion refers to Figure 3:
A storage vessel 24 is provided for staging an aqueous slurry of
relatively long papermaking fibers. The slurry is conveyed by means of a
pump 25 and optionally through a refiner 26 to fully develop the strength
potential of the long papermaking fibers. Additive pipe 27 conveys a resin
to provide for wet or dry strength, as desired in the finished product. The
slurry is then further conditioned in mixer 28 to aid in absorption of the
resin. The suitably conditioned slurry is then diluted with white water 29 in
a fan pump 30 forming a dilute long papermaking fiber slurry 31.
Optionally, pipe 32 conveys an flocculant to mix with slurry 31, forming an
aqueous flocculated long fiber papermaking slurry 33.
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31
Still referring to Figure 3, a storage vessel 34 is a repository for a fine
particulate filler slurry. Additive pipe 35 conveys an aqueous dispersion of a
anionic flocculant. Pump 36 acts to convey the fine particulate slurry as
well as provide for dispersion of the flocculant. The slurry is conditioned in
a mixer 37 to aid in absorption of the additive. Resultant slurry 38 is
conveyed to a point where it is mixed with an aqueous dispersion of short
papermaking fibers.
Still referring to Figure 3, a short papermaking fiber slurry originates
from a repository 39, from which it is conveyed through pipe 48 by pump
40 to a point where it mixes with the conditioned fine particulate filler
slurry
38 to become the short fiber based aqueous papermaking slurry 41. Pipe 46
conveys an aqueous dispersion of cationic starch which mixes with slurry
41, aided by in line mixer 50, to form flocculated slurry 47. White water 29
is directed into the flocculated slurry which mixes in fan pump 42 to become
the dilute flocculated short fiber based aqueous papermaking slurry 43.
Optionally, pipe 44 conveys additional flocculant to increase the level of
flocculation of dilute slurry 43 forming slurry 45.
Preferably, the short papermaking fiber slurry 45 from Figure 3 is
directed to the preferred papermaking process illustrated in Figure 1 and is
divided into two approximately equal streams which are then directed into
headbox chambers 82 and 83 ultimately evolving into off-Yankee-side-layer
75 and Yankee-side-layer 71, respectively of the strong, soft, low dusting,
filled creped tissue paper. Similarly, the long papermaking fiber slurry 33,
referring to Figure 3, is preferably directed into headbox chamber 82b
ultimately evolving into center layer 73 of the strong, soft, low dusting,
filled
creped tissue paper.
The Creped Papermaking Process
Figure 1 is a schematic representation illustrating a creped
papermaking process for producing a strong, soft, and low dusting filled
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creped tissue paper with biased surface bonding properties. These preferred
embodiments are described in the following discussion, wherein reference is
made to Figure 1.
Figure 1 is a side elevational view of a preferred papermaking machine
80 for manufacturing paper according to the present invention. Referring to
Figure 1, papermaking machine 80 comprises a layered headbox 81 having a
top chamber 82 a center chamber 82b, and a bottom chamber 83, a slice
roof 84, and a Fourdrinier wire 85 which is looped over and about breast roll
86, deflector 90, vacuum suction boxes 91, couch roll 92, and a plurality of
turning rolls 94. In operation, one papermaking furnish is pumped through
top chamber 82 a second papermaking furnish is pumped through center
chamber 82b, while a third furnish is pumped through bottom chamber 83
and thence out of the slice roof 84 in over and under relation onto
Fourdrinier wire 85 to form thereon an embryonic web 88 comprising layers
88a, and 88b, and 88c. Dewatering occurs through the Fourdrinier wire 85
and is assisted by deflector 90 and vacuum boxes 91. As the Fourdrinier
wire makes its return run in the direction shown by the arrow, showers 95
clean it prior to its commencing another pass over breast roll 86. At web
transfer zone 93, the embryonic web 88 is transferred to a foraminous
carrier fabric 96 by the action of vacuum transfer box 97. Carrier fabric 96
carries the web from the transfer zone 93 past vacuum dewatering box 98,
through blow-through predryers 100 and past two turning rolls 101 after
which the web is transferred to a Yankee dryer 108 by the action of
pressure roll 102. The carrier fabric 96 is then cleaned and dewatered as it
completes its loop by passing over and around additional turning rolls 101,
showers 103, and vacuum dewatering box 105. The predried paper web is
adhesively secured to the cylindrical surface of Yankee dryer 108 aided by
adhesive applied by spray applicator 109. Drying is completed on the steam
heated Yankee dryer 108 and by hot air which is heated and circulated
through drying hood 110 by means not shown. The web is then dry creped
from the Yankee dryer 108 by doctor blade 111 after which it is designated
paper sheet 70 comprising a Yankee-side layer 71 a center layer 73, and an
off-Yankee-side layer 75. Paper sheet 70 then passes between calendar
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rolls 112 and 113, about a circumferential portion of reel 1 15, and thence is
wound into a roll 116 on a core 117 disposed on shaft 118.
Still referring to Figure 1, the genesis of Yankee-side layer 71 of paper
sheet 70 is the furnish pumped through bottom chamber 83 of headbox 81,
and which furnish is applied directly to the Fourdrinier wire 85 whereupon it
becomes layer 88c of embryonic web 88. The genesis of the center layer
73 of paper sheet 70 is the furnish delivered through chamber 82.5 of
headbox 81, and which furnish forms layer 88b on top of layer 88c. The
genesis of the off-Yankee-side layer 75 of paper sheet 70 is the furnish
delivered through top chamber 82 of headbox 81, and which furnish forms
layer 88a on top of layer 88b of embryonic web 88. Although Figure 1
shows papermachine 80 having headbox 81 adapted to make a three-layer
web, headbox 81 may alternatively be adapted to make other multi-layered
tissue webs having different numbers of layers. One embodiment of the
present invention is achieved by relegating the fine particulate filler to the
furnish resulting in layer 88b; thereby increasing the retentive efficiency of
the papermaking process.
Further, with respect to making paper sheet 70 embodying the present
invention on papermaking machine 80, Figure 1, the Fourdrinier wire 85
must be of a fine mesh having relatively small spans with respect to the
average lengths of the fibers constituting the short fiber furnish so that
good
formation will occur; and the foraminous carrier fabric 96 should have a fine
mesh having relatively small opening spans with respect to the average
lengths of the fibers constituting the long fiber furnish to substantially
obviate bulking the fabric side of the embryonic web into the inter-
filamentary spaces of the fabric 96. Also, with respect to the process
conditions for making exemplary paper sheet 70, the paper web is
preferably dried to about 80% fiber consistency, and more preferably to
about 95% fiber consistency prior to creping.
The present invention is applicable to creped tissue paper in general,
including but not limited to conventionally felt-pressed creped tissue paper;
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high bulk pattern densified creped tissue paper; and high bulk, uncompacted
creped tissue paper.
The filled creped tissue paper webs of the present invention have a
basis weight of between 10 g!m2 and about 100 glm2. tn its preferred
embodiment, the filled tissue paper of the present invention has a basis
weight between about 10 g/m2 and about 50 glm2 and, most preferably,
between about 10 g/m2 and about 30 g/m2. Creped tissue paper webs
suitable for the present invention possess a density of about 0.60 g/cm3 or
less. In its preferred embodiment, the fitted tissue paper of the present
invention has a density between about 0.03 g/m3 and about 0.6 g/m3 and,
most preferably, between about 0.05 glm3 and 0.2 g/m3.
The present invention is further applicable to multi-layered tissue
paper webs. Tissue structures farmed from layered paper webs are
described in U.S. Patent 3,994.771, Morgan, Jr. et at. issued November 30,
1976, U.S. Patent No. 4,300.981, Carstens, issued November 17, 1981,
U.S. Patent No. 4,166.001, Dunning et al., issued August 28. 1979, and
European Patent Publication No. 0 613 979 A1, Edwards et at., published
September 7, 1994. The layers are preferably comprised of different fiber
types, the fibers typically being relatively long softwood and relatively
short
hardwood fibers as used in multi-layered tissue paper making. Multi-layered
tissue paper webs suitable for the present invention comprise at least two
superposed layers, an inner layer and at least one outer layer contiguous with
the inner layer. Preferably, the mufti-layered tissue papers comprise three
superposed layers, an inner or center layer, and two outer layers, a Yankee
side outer layer and an off-Yankee side outer layer with the inner layer
located
between the two outer layers. The Yankee side outer layer is so named
because it forms the surface which contacts the Yankee dryer surface. The
two outer layers preferably comprise a primary filamentary constituent of
relatively short paper making fibers having an average fiber length between
about 0.5 and about 1.5 mm, preferably less than about 1.0 mm. These short
paper making fibers typically comprise hardwood fibers, preferably hardwood
Kraft fibers, and most preferably derived from eucalyptus. The inner layer
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preferably comprises a primary filamentary constituent of relatively long
paper making fibers having an average fiber length of least about 2.0 mm.
These long paper making fibers are typically softwood fibers, preferably,
northern softwood Kraft fibers. Preferably, the majority of the particulate
filler of the present invention is contained in at least one of the outer
layers
of the multi-layered tissue paper web of the present invention. In one
embodiment of the present invention, the majority of the particulate filler of
the present invention is contained in both of the outer layers. In another
embodiment of the present invention, the majority of the particulate filler is
contained in one of the outer layers; specifically, in the outer layer
originating at greatest distance from the foraminous surface, i.e. the off-
Yankee side outer layer.
The creped tissue paper products made from multi-layered creped
tissue paper webs can be single-ply tissue products or multi-ply tissue
products.
The equipment and methods are well known to those skilled in the art.
In a typical process, a low consistency pulp furnish is provided in a
pressurized headbox. The headbox has an opening for delivering a thin
deposit of pulp furnish onto the Fourdrinier wire to form a wet web. The
web is then typically dewatered to a fiber consistency of between about ~%
and about 25 % (total web weight basis) by vacuum dewatering.
To prepare filled tissue paper products according to those disclosed in
the present invention, an aqueous papermaking furnish is deposited on a
foraminous surface to form an embryonic web. The scope of the invention
also includes tissue paper products resultant from the formation of multiple
paper layers in which two or more layers of furnish are preferably formed
from the deposition of separate streams of dilute fiber slurries for example
in
a multi-channeled headbox. The layers are preferably comprised of different
fiber types, the fibers typically being relatively long softwood and
relatively
short hardwood fibers as used in multi-layered tissue paper making. If the
individual layers are initially formed on separate wires, the layers are
subsequently combined when wet to form a multi-layered tissue paper web.
The papermaking fibers are preferably comprised of different fiber types, the
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fibers typically being relatively long softwood and relatively short hardwood
fibers. More preferably, the hardwood fibers comprise at least about 50%
and said softwood fibers comprise at least about 10% of said papermaking
fibers.
In the papermaking process used to make filled tissue products
according to the present invention, the step comprising the transfer of the
web to a felt or fabric, e.g., conventionally felt pressing tissue paper, well
known in the art, is expressly included within the scope of this invention. In
this process step, the web is dewatered by transferring to a dewatering felt
and pressing the web so that water is removed from the web into the felt by
pressing operations wherein the web is subjected to pressure developed by
opposing mechanical members, for example, cylindrical rolls. Because of the
substantial pressures needed to de-water the web in this fashion, the
resultant webs made by conventional felt pressing are relatively high in
density and are characterized by having a uniform density throughout the
web structure.
In the papermaking process used to make filled tissue products
according to the present invention, the step comprising the transfer of the
semi-dry web to a Yankee dryer, the web is pressed during transfer to the
cylindrical steam drum apparatus known in the art as a Yankee dryer. The
side of web pressed against the Yankee dryer is referred to herein as the
Yankee side outer layer, wheras the side facing away fro the Yankee dryer is
referred to herein as the off-Yankee side outer layer. The transfer is
effected by mechanical means such as an opposing cylindrical drum pressing
against the web. Vacuum may also be applied to the web as it is pressed
against the Yankee surface. Multiple Yankee dryer drums can be employed.
More preferable variations of the papermaking process for making
filled tissue papers include the so-called pattern densified methods in which
the resultant structure is characterized by having a relatively high bulk
field
of relatively low fiber density and an array of densified zones of relatively
high fiber density dispersed within the high bulk field. The high bulk field
is
alternatively characterized as a field of pillow regions. The densified zones
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are alternatively referred to as knuckle regions. The densified zones may be
discretely spaced within the high bulk field or may be interconnected, either
fully or partially, within the high bulk field. Preferably, the Zones of
relatively high density are continuous and the high bulk field is discrete.
Preferred processes for making pattern densified tissue webs are disclosed
in U.S. Patent No. 3.301,746. issued to Sanford and Sisson on January 31,
1967, U.S. Patent No. 3,974,025, issued to Peter G. Avers on August 10,
1976, and U.S. Patent No. 4,191.609, issued to Paul D. Trokhan on March
4, 1980, and U.S. Patent 4,637,859, issued to Paul D. Trokhan on January
20, 1987, U.S. Patent 4.942.077 issued to Wendt et al. on July 17, 1990.
European Patent Publication No. 0 617 164 A1, Hyland et al., published
September 28, 1994, European Patent Publication No. 0 616 074 A1,
Hermans et al., published September 21, 1994,
To form pattern densified webs, the web transfer step immediately
after forming the web is to a forming fabric rather than a felt. The web is
juxtaposed against an array of supports comprising the forming fabric. The
web is pressed against the array of supports, thereby resulting in densified
zones in the web at the locations geographically corresponding to the points
of contact between the array of supports and the wet web. The remainder
of the web not compressed during this operation is referred to as the high
bulk field. This high bulk field can be further dedensified by application of
fluid pressure, such as with a vacuum type device or a blow-through dryer.
The wsb is dewatered, and optionally predried, in such a manner so as to
substantially avoid compression of the high bulk field. This is preferably
accomplished by fluid pressure, such as with a vacuum type device or blow-
through dryer, or alternately by mechanically pressing the web against an
array of supports wherein the high bulk field is not compressed. The
operations of dewatering, optional predrying and formation of the densified
zones may be integrated or partially integrated to reduce the total number of
processing steps performed. The moisture content of the semi-dry web at
the point of transfer to the Yankee surface is less than about 409 and the
hot air is forced through said semi-dry web while the semi-dry web is on
said forming fabric to form a low density structure.
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The pattern densified web is uansferred to the Yankee dryer and dried
to completion, preferably still avoiding mechanical pressing. In the present
invention, preferably from about 8°!o to about 55% of the creped tissue
paper surface comprises densified knuckles having a relative density of at
feast 125° of the density of the high bulk field.
The array of supports is preferably an imprinting carrier fabric having a
patterned displacement of knuckles which operate as the array of supports
which facilitate the formation of the densified zones upon application of
pressure. The pattern of knuckles constitutes the array of supports
previously referred to. Imprinting carrier fabrics are disclosed in U.S.
Patent
No. 3.301,746, Sanford and Sisson, issued January 31, 1967, U.S. Patent
No. 3,821,068, Salvucci, Jr. et al., issued May 21. 1974, U.S. Patent No.
3,974,025, Ayers, issued August 10. 1976, U.S. Patent No. 3,573,164,
Friedberg et al., issued March 30, 1971, U.S. Patent No.. 3,473,576.
Amneus. issued October 21, 1969, U.S. Patent No. 4,239.065. Trokhan,
issued December 1 fi, 1980, and U.S. Patent No. 4,528.239, Trokhan,
issued July 9, 1985.
Most preferably, the embryonic web is caused to conform to the
surface of an open mesh drying/imprinting fabric by the application of a fluid
force to the web and thereafter thermally predried on said fabric as part of a
low density paper making process.
Another variation of the processing steps included within the present
invention includes the formation of, so-called uncompscted, non pattern-
densified mufti-layered tissue paper structures such as are described in U.S.
Patent No. 3.812,000 issued to Joseph L. Salvucci, Jr. and Peter N.
Yiannos on May 21. 1974 and U.S. Patent No. 4,208,459, issued to Henry
E. Becker, Albert L. McConnell, and Richard Schutte on June 17, 1980.
In general uncompacted, non pattern densified mufti-layered tissue paper
structures are prepared by depositing a paper making furnish on a foraminous
forming wire such as a Fourdrinier wire to form a wet web, draining the web
and removing
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additional water without mechanical compression until the web has a fiber'
' consistency of at least 80%, and creping the web. Water is removed from
the web by vacuum dewatering and thermal drying. The resulting structure
is a soft but weak high bulk sheet of relatively uncompacted fibers. Bonding
material is preferably applied to portions of the web prior to creping.
The advantages related to the practice of the present invention
include the ability to reduce the amount of papermaking fibers required to
produce a given amount of tissue paper product. Further, the optical
properties, particularly the opacity, of the tissue product are improved.
These advantages are realized in a tissue paper web which has a high level
of strength and is low dusting.
The term "opacity" as used herein refers to the resistance of a tissue
paper web from transmitting light of a wavelength corresponding to the
visible portion of the electromagnetic spectrum. The "specific opacity" is
the measure of the degree of opacity imparted for each 1 g/m2 unit of basis
weight of a tissue paper web. The method of measuring opacity and
calculating specific opacity are detailed in a later section of this
specification. Tissue paper webs according to the present invention
preferably have more than about 5%, more preferably more than about
5.5%, and most preferably more than about 6% specific opacity.
The term "strength" as used herein refers to the specific total tensile
strength, the determination method for this measure is included in a later
section of this specification. The tissue paper webs according to the
present invention are strong. This generally means that their specific total
tensile strength is at least about 0.25 meters, more preferably more than
about 0.40 meters.
The terms "lint" and "dust" are used interchangeably herein and refer
to the tendency of a tissue paper web to release fibers or particulate fillers
as measured in a controlled abrasion test, the methodology for which is
detailed in a later section of this specification. Lint and dust are related
to
strength since the tendency to release fibers or particles is directly related
to
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the degree to which such fibers or particles are anchored into the structure.
As the overall level of anchoring is increased, the strength will be
increased. '
However, it is possible to have a level of strength which is regarded as
acceptable but have an unacceptable level of tinting or dusting. This is
because tinting or dusting can be localized. For example, the surface of a
tissue paper web can be prone to tinting or dusting, while the degree of
bonding beneath the surface can be sufficient to raise the overall level of
strength to quite acceptable levels. In another case, the strength can be
derived from a skeleton of relatively long papermaking fibers, while fiber
fines or the particulate filler can be insufficiently bound within the
structure.
The filled tissue paper webs according to the present invention are relatively
low in lint. Ultimate lint values, representing the average of lint values of
the Yankee-side and the off-Yankee side, below about 12 are preferable;
below about 10 are more preferable; and below 8 are most preferable.
The multi-layered tissue paper web of this invention can be used in
any application where soft, absorbent multi-layered tissue paper webs are
required. Particularly advantageous uses of the multi-layered tissue paper
web of this invention are in toilet tissue and facial tissue products. Both
single-ply and multi-ply tissue paper products can be produced from the
webs of the present invention.
The Soft Filled Tissue Paper with Biased Surface Properties
Figure 4 is a schematic representation of one embodiment of the soft
tissue paper of the present invention revealing the structure of the various
layers of the creped tissue paper.
Referring to Figure 4, inner layer 120 is located between Yankee side
layer 121 and off-Yankee side layer 122. Inner layer 120 predominately
contains softwood fibers 123, while each of the outer layers 121 and 122
predominantly contain hardwood fibers, 125.
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Fine particulate filler particles 124 are preferably located in outer
layers 121 and 122, and, particularly in one aspect of the invention are
restricted as far as practical to the layer 122.
The degree of bonding in layer 121 is controlled to be less than in
layer 122 such that the lint value when measured with respect to layer 121
is higher than when measured with respect to layer 122. This is
accomplished by promoting less bonding in layer 121 relative to layer 122.
Those skilled in the art will recognize specific means by which this can be
accomplished. Examples of means include refining the furnish composition
for layer 121 to less degree, using less binder such as starch in layer 121,
or by adding a bond inhibiting agent to layer 121 .
Analytical and Testing Procedures
A. Density
The density of multi-layered tissue paper, as that term is used herein,
is the average density calculated as the basis weight of that paper divided
by the caliper, with the appropriate unit conversions incorporated therein.
Caliper of the multi-layered tissue paper, as used herein, is the thickness of
the paper when subjected to a compressive load of 95 g/in2 (15.5 g/cm2).
B. Molecular Weight Determination
The essential distinguishing characteristic of polymeric materials is
their molecular size. The properties which have enabled polymers to be
used in a diversity of applications derive almost entirely from their macro-
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molecular nature. In order to characterize fully these materials it is
essential
to have some means of defining and determining their molecular weights and
molecular weight distributions. It is more correct to use the term relative
molecular mass rather the molecular weight, but the latter is used more
generally in polymer technology. It is not always practical to determine
molecular weight distributions. However, this is becoming more common
practice using chromatographic techniques. Rather, recourse is made to
expressing molecular size in terms of molecular weight averages.
Molecular Weight Averages
If we consider a simple molecular weight distribution which represents
the weight fraction (wi) of molecules having relative molecular mass (Mi), it
is possible to define several useful average values. Averaging carried out on
the basis of the number of molecules (N;) of a particular size (Mi) gives the
Number Average Molecular Weight
n - ~'t Ni Mi
~ Ni
An important consequence of this definition is that the Number
Average Molecular Weight in grams contains Avogadro°s Number of
molecules. This definition of molecular weight is consistent with that of
monodisperse molecular species, i.e. molecules having the same molecular
weight. Of more significance is the recognition that if the number of
molecules in a given mass of a potydisperse polymer can be determined in
some way then n, can be calculated readily. This is the basis of colligative
property measurements.
Averaging on the basis of the weight fractions (Wi) of molecules of a
given mass (Mi) leads to the definition of Weight Average Molecular Weights
w - -- SJt Wi Ni-= ~Jt Ni Mi2
~J? Wi ~Jt Ni Mi
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"" is a more useful means for expressing polymer molecular weights
than n since it reflects more accurately such properties as melt viscosity and
mechanical properties of polymers and is therefor used in the present
invention.
C. Filler Particle Size Determination
Particle size is an important determinant of performance of filter,
especially as it relates to the ability to retain it in a paper sheet. Cfay
particles, in particular, are platy or blocky, not spherical, but a measure
referred to as "equivalent spherical diameter" can be used as a relative
measure of odd shaped particles and this is one of the main methods that
the industry uses to measure the particle size of clays and other particulate
fillers. Equivalent spherical diameter determinations of fillers can be made
using TAPPI Useful Method 655, which is based on the Sedigraph°
analysis,
i.e., by the instrument of such type available from the Micromeritics
Instrument Corporation of Norcross, Georgia. The instrument uses soft x-
rays to determine gravity sedimentation rate of a dispersed slurry of
particulate filler and employs Stokes Law to calculate the equivalent
spherical diameter.
D. Filler Quantitative Analysis in Paper
Those skilled in the art will recognize that there are many methods for
quantitative analysis of non-cellulosic filler materials in paper. To aid in
the
practice of this invention, two methods will be detailed applicable to the
most preferred inorganic type fillers. The first method, asking, is applicable
to inorganic fillers in general. The second method, determination of kaolin
by XRF, is tailored specifically to the filler found particularly suitable in
the
practice of the present invention, i.e. kaolin.
Asking
Asking is performed by use of a muffle furnace. In this method, a four
place balance is first cleaned, calibrated and tarred. Next, a clean and
empty platinum dish is weighed on the pan of the four place balance.
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Record the weight of the empty platinum dish in units of grams to the ten-
thousandths place. Without re-tarring the balance, approximately 10 grams
of the filled tissue paper sample is carefully folded into the platinum dish.
The weight of the platinum boat and paper is recorded in units of grams to
the ten-thousandths place.
The paper in the platinum dish is then pre-ashed at low temperatures
with a Bunsen burner flame. Care must be taken to do this slowly to avoid
the formation of air-borne ash. If air-borne ash is observed, a new sample
must be prepared. After the flame from this pre-ashing step has subsided,
place the sample in the muffle furnace. The muffle furnace should be at a
temperature of 575 C. Allow the sample to completely ash in the muffle
furnace for approximately 4 hours. After this time, remove the sample with
thongs and place on a clean, flame retardant surface. Allow the sample to
cool for 30 minutes. After cooling, weigh the platinum dish/ash combination
in units of grams to the ten-thousandths place. Record this weight.
The ash content in the filled tissue paper is calculated by subtracting
the weight of the clean, empty platinum dish from the weight of the
platinum dish/ash combination. Record this ash content weight in units of
grams to the ten-thousandths place.
The ash content weight may be converted to a filler weight by
knowledge of the filler loss on ashing (due for example to water vapor loss
in kaolin). To determine this, first weigh a clean and empty platinum dish on
the pan of a four place balance. Record the weight of the empty platinum
dish in units of grams to the ten-thousandths place. Without re-tarring the
balance, approximately 3 grams of the filler is carefully poured into the
platinum dish. The weight of the platinum dish/filler combination is recorded
in units of grams to the ten-thousandths place.
This sample is then carefully placed in the muffle furnace at 575 C.
Allow the sample to completely ash in the muffle furnace for approximately
4 hours. After this time, remove the sample with thongs and place on a
clean, flame retardant surface. Allow the sample to cool for 30 minutes.
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After cooling, weigh the platinum dish/ash combination in units of grams to
the ten-thousandths place. Record this weight.
Calculate the percent loss on asking in the original filler sample using
the following equation:
96 Loss on asking = [(Wt of Ori4inal Filler Sample&ot dish) IWt of Filler
Ash&ot dishll x 10_0
[(Wt. of Original Filler Sample&pt dish) - (Wt of pt dish)]
The % loss on asking in kaolin is 10 to 15%. The original ash weight in
units of grams can then be converted to a filler weight in units of grams
with the following equation:
Weight of Filler (g) = Weight of Ash (c1)
t1 - (% Loss on Ashing/100)~
The percent filler in the original filled tissue paper can then be calculated
as
follows:
96 Filler in Tissue Paper = Weioht of Filler (s~l x 100
[(Weight of Platinum Dish&Paper) - (Weight of Platinum Dish)1
Determination of Kaolin Clay by XRF
The main advantage of the XRF technique over the muffle furnace
asking technique is speed, but it is not as universally applicable. The XRF
spectrometer can quantitate the level of kaolin clay in a paper sample within
5 minutes compared to the hours it takes in the muffle furnace asking
method.
The X-ray Fluorescence technique is based on the bombardment of
the sample of interest with X-ray photons from a X-ray tube source. This
bombardment by high energy photons causes core level electrons to be
photoemitted by the elements present in the sample. These empty core
levels are then filled by outer shell electrons. This filling by the outer
shell
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electrons results in the fluorescence process such that additional X-ray
photons are emitted by the elements present in the sample. Each element
has distinct "fingerprint" energies for these X-ray fluorescent transitions.
The energy and thus the identity of the element of interest of these emitted
X-ray fluorescence photons is determined with a lithium doped silicon
semiconductor detector. This detector makes it possible to determine the
energy of the impinging photons and thus the identity the elements present
in the sample. The elements from sodium to uranium may be identified in
most sample matrices.
In the case of the clay fillers, the detected elements are both silicon
and aluminum. The particular X-ray Fluorescence instrument used in this
clay analysis is a Spectrace 5000 made by Baker-Hughes Inc. of Mountain
View, California. The first step in the quantitative analysis of clay is to
calibrate the instrument with a set of known clay filled tissue standards,
using clay inclusions ranging from 8% to 20%, for example.
The exact clay level in these standard paper samples is determined
with the muffle furnace ashing technique described above. A blank paper
sample is also included as one of the standards. At least 5 standards
bracketing the desired target clay level should be used to calibrate the
instrument.
Before the actual calibration process, the X-ray tube is powered to
settings of 13 kilovolts and 0.20 milliamps. The instrument is also set up to
integrate the detected signals for the aluminum and silicon contained in the
clay. The paper sample is prepared by first cutting a 2" by 4" strip. This
strip is then folded to make a 2'° X 2°' with the off-Yankee
side facing out.
This sample is placed on top of the sample cup and held in place with a
retaining ring. During sample preparation, care must be taken to keep the
sample flat on top of the sample cup. The instrument is then calibrated
using this set of known standards.
After calibrating the instrument with the set of known standards, the
linear calibration curve is stored in the computer system's memory. This
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linear calibration curve is used to calculate clay levels in the unknowns. To
insure the X-ray Fluorescence system is stable and working properly, a
check sample of known clay content is run with every set of unknowns. If
the analysis of the check sample results in an inaccurate result (10 to 15%
off from its known clay content), the instrument is subjected to trouble-
shooting and/or re-calibrated.
For every paper-making condition, the clay content in at least 3
unknown samples is determined. The average and standard deviation is
taken for these 3 samples. If the clay application procedure is suspected or
intentionally set up to vary the clay content in either the cross direction
(CD)
or machine direction (MD) of the paper, more samples should be measured
in these CD and MD directions.
E. Measurement of Tissue Paper Lint
The amount of lint generated from a tissue product is determined with
a Sutherland Rub Tester. This tester uses a motor to rub a weighted felt 5
times over the stationary toilet tissue. The Hunter Color L value is measured
before and after the rub test. The difference between these two Hunter
Color L values is calculated as lint.
SAMPLE PREPARATION:
Prior to the lint rub testing, the paper samples to be tested should he
conditioned according to Tappi Method #T4020M-88. Here, samples are
preconditioned for 24 hours at a relative humidity level of 10 to 35% and
within a temperature range of 22 to 40 °C. After this preconditioning
step,
samples should be conditioned for 24 hours at a relative humidity of 48 to
52% and within a temperature range of 22 to 24 °C. This rub testing
should also take place within the confines of the constant temperature and
humidity room.
The Sutherland Rub Tester may be obtained from Testing Machines,
Inc. (Amityville, NY, 11701 ). The tissue is first prepared by removing and
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discarding any product which might have been abraded in handling, e.g. on
the outside of the roll. For multi-ply finished product, three sections with
each containing two sheets of multi-ply product are removed and set on the
bench-top. For single-ply product, six sections with each containing two
sheets of single-ply product are removed and set on the bench-top. Each
sample is then folded in half such that the crease is running along the cross
direction (CD) of the tissue sample. For the multi-ply product, make sure
one of the sides facing out is the same side facing out after the sample is
folded. In other words, do not tear the plies apart from one another and rub
test the sides facing one another on the inside of the product. For the
single-ply product, make up 3 samples with the off-Yankee side out and 3
with the Yankee side out. Keep track of which samples are Yankee side out
and which are off-Yankee side out.
Obtain a 30°' X 40" piece of Crescent #300 cardboard from Cordage
Inc. (800 E. Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut
out six pieces of cardboard of dimensions of 2.5" X 6°'. Puncture two
holes
into each of the six cards by forcing the cardboard onto the hold down pins
of the Sutherland Rub tester.
If working with single-ply finished product, center and carefully place
each of the 2.5°' X 6" cardboard pieces on top of the six previously
folded
samples. Make sure the 6" dimension of the cardboard is running parallel to
the machine direction (MD) of each of the tissue samples. If working with
multi-ply finished product, only three pieces of the 2.5" X 6°'
cardboard will
be required. Center and carefully place each of the cardboard pieces on top
of the three previously folded samples. Once again, make sure the 6"
dimension of the cardboard is running parallel to the machine direction (MD)
of each of the tissue samples.
Fold one edge of the exposed portion of tissue sample onto the back
of the cardboard. Secure this edge to the cardboard with adhesive tape
obtained from 3M Inc. (3/4" wide Scotch Brand, St. Paul, MN). Carefully
grasp the other over-hanging tissue edge and snugly fold it over onto the
back of the cardboard. While maintaining a snug fit of the paper onto the
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board, tape this second edge to the back of the cardboard. Repeat this
procedure for each sample.
Turn over each sample and tape the cross direction edge of the tissue
paper to the cardboard. One half of the adhesive tape should contact the
tissue paper while the other half is adhering to the cardboard. Repeat this
procedure for each of the samples. If the tissue sample breaks, tears, or
becomes frayed at any time during the course of this sample preparation
procedure, discard and make up a new sample with a new tissue sample
strip.
If working with mufti-ply converted product, there will now be 3
samples on the cardboard. For single-ply finished product, there will now be
3 off-Yankee side out samples on cardboard and 3 Yankee side out samples
on cardboard.
FELT PREPARATION:
Obtain a 30" X 40" piece of Crescent #300 cardboard from Cordage
Inc. (800 E. Ross Road, Cincinnati, Ohio, 45217). Using a paper cutter, cut
out six pieces of cardboard of dimensions of 2.25" X 7.25". Draw two lines
parallel to the short dimension and down 1.125" from the top and bottom
most edges on the white side of the cardboard. Carefully score the length
of the line with a razor blade using a straight edge as a guide. Score it to a
depth about half way through the thickness of the sheet. This scoring
allows the cardboard/felt combination to fit tightly around the weight of the
Sutherland Rub tester. Draw an arrow running parallel to the long dimension
of the cardboard on this scored side of the cardboard.
Cut the six pieces of black felt (F-55 or equivalent from New England
Gasket, 550 Broad Street, Bristol, CT 06010) to the dimensions of 2.25" X
8.5" X 0.0625." Place the felt on top of the unscored, green side of the
cardboard such that the long edges of both the felt and cardboard are
parallel and in alignment. Make sure the fluffy side of the felt is facing up.
Also allow about 0.5" to overhang the top and bottom most edges of the
cardboard. Snugly fold over both overhanging felt edges onto the backside
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of the cardboard with Scotch brand tape. Prepare a total of six of these
felt/cardboard combinations.
For best reproducibility, all samples should be run with the same lot of
felt. Obviously, there are occasions where a single lot of felt becomes
completely depleted. In those cases where a new lot of felt must be
obtained, a correction factor should be determined for the new lot of felt.
To determine the correction factor, obtain a representative single tissue
sample of interest, and enough felt to make up 24 cardboard/felt samples
for the new and old lots.
As described below and before any rubbing has taken place, obtain
Hunter L readings for each of the 24 cardboard/felt samples of the new and
old lots of felt. Calculate the averages for both the 24 cardboard/felt
samples of the old lot and the 24 cardboard/felt samples of the new lot.
Next, rub test the 24 cardboard/felt boards of the new lot and the 24
cardboard/felt boards of the old lot as described below. Make sure the
same tissue lot number is used for each of the 24 samples for the old and
new lots. In addition, sampling of the paper in the preparation of the
cardboard/tissue samples must be done so the new lot of felt and the old lot
of felt are exposed to as representative as possible of a tissue sample. For
the case of 1-ply tissue product, discard any product which might have
been damaged or abraded. Next, obtain 48 strips of tissue each two usable
units (also termed sheets) long. Place the first two usable unit strip on the
far left of the lab bench and the last of the 48 samples on the far right of
the bench. Mark the sample to the far left with the number °' 1
°' in a 1 cm
by 1 cm area of the corner of the sample. Continue to mark the samples
consecutively up to 48 such that the last sample to the far right is numbered
48.
Use the 24 odd numbered samples for the new felt and the 24 even
numbered samples for the old felt. Order the odd number samples from
lowest to highest. Order the even numbered samples from lowest to
highest. Now, mark the lowest number for each set with a letter "Y." Mark
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the next highest number with the letter "O." Continue marking the samples
in this alternating "Y"/"O" pattern. Use the "Y" samples for Yankee side out
lint analyses and the "O" samples for off-Yankee side lint analyses. For 1-
ply product, there are now a total of 24 samples for the new lot of felt and
the old lot of felt. Of this 24, twelve are for Yankee side out lint analysis
and 12 are for off-Yankee side lint analysis.
Rub and measure the Hunter Color L values for all 24 samples of the
old felt as described below. Record the 12 Yankee side Hunter Color L
values for the old felt. Average the 12 values. Record the 12 off-Yankee
side Hunter Color L values for the old felt. Average the 12 values. Subtract
the average initial un-rubbed Hunter Color L felt reading from the average
Hunter Color L reading for the Yankee side rubbed samples. This is the
delta average difference for the Yankee side samples. Subtract the average
initial un-rubbed Hunter Color L felt reading from the average Hunter Color L
reading for the off-Yankee side rubbed samples. This is the delta average
difference for the off-Yankee side samples. Calculate the sum of the delta
average difference for the Yankee-side and the delta average difference for
the off-Yankee side and divide this sum by 2. This' is the uncorrected lint
value for the old felt. If there is a current felt correction factor for the
old
felt, add it to the uncorrected lint value for the old felt. This value is the
corrected Lint Value for the old felt.
Rub and measure the Hunter Color L values for all 24 samples of the
new felt as described below. Record the 12 Yankee side Hunter Color L
values for the new felt. Average the 12 values. Record the 12 off-Yankee
side Hunter Color L values for the new felt. Average the 12 values.
Subtract the average initial un-rubbed Hunter Color L felt reading from the
average Hunter Color L reading for the Yankee side rubbed samples. This is
the delta average difference for the Yankee side samples. Subtract the
average initial un-rubbed Hunter Color L felt reading from the average Hunter
Color L reading for the oft-Yankee side rubbed samples. This is the delta
average difference for the off-Yankee side samples. Calculate the sum of
the delta average difference for the Yankee-side and the delta average
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difference for the off-Yankee side and divide this sum by 2. This is the ,
uncorrected lint value for the new felt.
Take the difference between the corrected Lint Value from the old felt
and the uncorrected lint value for the new felt. This difference is the felt
correction factor for the new lot of felt.
Adding this felt correction factor to the uncorrected lint value for the
new felt should be identical to the corrected Lint Value for the old felt.
The same type procedure is applied to two-ply tissue product with 24
samples run for the old felt and 24 run for the new felt. But, only the
consumer used outside layers of the plies are rub tested. As noted above,
make sure the samples are prepared such that a representative sample is
obtained for the old and new felts.
BARE OF 4 POUND WEIGHT:
The four pound weight has four square inches of effective contact
area providing a contact pressure of one pound per square inch. Since the
contact pressure can be changed by alteration of the rubber pads mounted
on the face of the weight, it is important to use only the rubber pads
supplied by the manufacturer (Brown Inc., Mechanical Services Department,
Kalamazoo, MI). These pads must be replaced if they become hard, abraded
or chipped off.
When not in use, the weight must be positioned such that the pads
are not supporting the full weight of the weight. It is best to store the
weight on its side.
RUB TESTER INSTRUMENT CALIBRATION:
The Sutherland Rub Tester must first be calibrated prior to use. First,
turn on the Sutherland Rub Tester by moving the tester switch to the "cont"
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position. When the tester arm is in its position closest to the user, turn the
tester's switch to the "auto" position. Set the tester to run 5 strokes by
moving the pointer arm on the large dial to the "five" position setting. One
stroke is a single and complete forward and reverse motion of the weight.
The end of the rubbing block should be in the position closest to the
operator at the beginning and at the end of each test.
Prepare a tissue paper on cardboard sample as described above. in
addition, prepare a felt on cardboard sample as described above. Both of
these samples will be used for calibration of the instrument and will not be
used in the acquisition of data for the actual samples.
Place this calibration tissue sample on the base plate of the tester by
slipping the holes in the board over the hold-down pins. The hold-down pins
prevent the sample from moving during the test. Clip the calibration
felt/cardboard sample onto the four pound weight with the cardboard side
contacting the pads of the weight. Make sure the cardboard/felt
combination is resting flat against the weight. Hook this weight onto the
tester arm and gently place the tissue sample underneath the weight/felt
combination. The end of the weight closest to the operator must be over
the cardboard of the tissue sample and not the tissue sample itself. The felt
must rest flat on the tissue sample and must be in 100% contact with the
tissue surface. Activate the tester by depressing the "push" button.
Keep a count of the number of strokes and observe and make a
mental note of the starting and stopping position of the felt covered weight
in relationship to the sample. If the total number of strokes is five and if
the
end of the felt covered weight closest to the operator is over the cardboard
of the tissue sample at the beginning and end of this test, the tester is
calibrated and ready to use. If the total number of strokes is not five or if
the end of the felt covered weight closest to the operator is over the actual
paper tissue sample either at the beginning or end of the test, repeat this
calibration procedure until 5 strokes are counted the end of the felt covered
weight closest to the operator is situated over the cardboard at the both the
start and end of the test.
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During the actual testing of samples, monitor and observe the stroke
count and the starting and stopping point of the felt covered weight.
Recalibrate when necessary.
HUNTER COLOR METER CALIBRATION:
Adjust the Hunter Color Difference Meter for the black and white
standard plates according to the procedures outlined in the operation manual
of the instrument. Also run the stability check for standardization as well as
the daily color stability check if this has not been done during the past
eight
hours. In addition, the zero reflectance must be checked and readjusted if
necessary.
Place the white standard plate on the sample stage under the
instrument port. Release the sample stage and allow the sample plate to be
raised beneath the sample port.
Using the "L-Y", "a-X°', and °'b-Z" standardizing knobs,
adjust the
instrument to read the Standard White Plate Values of "L",
'°a'°, and "b"
when the '°L", "a'°, and "b" push buttons are depressed in turn.
MEASUREMENT OF SAMPLES:
The first step in the measurement of lint is to measure the Hunter
color values of the black felt/cardboard samples prior to being rubbed on the
toilet tissue. The first step in this measurement is to lower the standard
white plate from under the instrument port of the Hunter color instrument.
Center a felt covered cardboard, with the arrow pointing to the back of the
color meter, on top of the standard plate. Release the sample stage,
allowing the felt covered cardboard to be raised under the sample port.
Since the felt width is only slightly larger than the viewing area
diameter, make sure the felt completely covers the viewing area. After
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confirming complete coverage, depress the L push button and wait for the
reading to stabilize. Read and record this L value to the nearest 0.1 unit.
If a D25D2A head is in use, lower the felt covered cardboard and
plate, rotate the felt covered cardboard 90 degrees so the arrow points to
the right side of the meter. Next, release the sample stage and check once
more to make sure the viewing area is completely covered with felt.
Depress the L,push button. Read and record this value to the nearest 0.1
unit. For the D25D2M unit, the recorded value is the Hunter Color L value.
For the D25D2A head where a rotated sample reading is also recorded, the
Hunter Color L value is the average of the two recorded values.
Measure the Hunter Color L values for all of the felt covered
card boards using this technique. If the Hunter Color L values are all within
0.3 units of one another, take the average to obtain the initial L reading. If
the Hunter Color L values are not within the 0.3 units, discard those
felt/cardboard combinations outside the limit. Prepare new samples and
repeat the Hunter Color L measurement until all samples are within 0.3 units
of one another.
For the measurement of the actual tissue paper/cardboard
combinations, place the tissue sample/cardboard combination on the base
plate of the tester by slipping the holes in the board over the hold-down
pins. The hold-down pins prevent the sample from moving during the test.
Clip the calibration felt/cardboard sample onto the four pound weight with
the cardboard side contacting the pads of the weight. Make sure the
cardboard/felt combination is resting flat against the weight. Hook this
weight onto the tester arm and gently place the tissue sample underneath
the weight/felt combination. The end of the weight closest to the operator
must be over the cardboard of the tissue sample and not the tissue sample
itself. The felt must rest flat on the tissue sample and must be in 100%
contact with the tissue surface.
Next, activate the tester by depressing the "push" button. At the end
of the five strokes the tester will automatically stop. Note the stopping
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position of the felt covered weight in relation to the sample. If the end of
the felt covered weight toward the operator is over cardboard, the tester is
operating properly. If the end of the felt covered weight toward the .
operator is over sample, disregard this measurement and recalibrate as
directed above in the Sutherland Rub Tester Calibration section.
Remove the weight with the felt covered cardboard. Inspect the
tissue sample. If torn, discard the felt and tissue and start over. !f the
tissue sample is intact, remove the felt covered cardboard from the weight.
Determine the Hunter Color L value on the felt covered cardboard as
described above for the blank felts. Record the Hunter Color L readings for
the felt after rubbing. Rub, measure, and record the Hunter Color L values
for all remaining samples.
After all tissues have been measured, remove and discard all felt.
Felts strips are not used again. Card boards are used until they are bent,
torn, limp, or no longer have a smooth surface.
CALCULATIONS:
Determine the delta L values by subtracting the average initial L
reading found for the unused felts from each of the measured values for the
off-Yankee and Yankee sides of the sample. Recall, multi-ply-ply product
will only rub one side of the paper. Thus, three delta L values will be
obtained for the multi-ply product. Average the three delta L values and
subtract the felt factor from this final average. This final result is termed
the
lint for the fabric side of the 2-ply product.
For the single-ply tissue web where both Yankee side and off-Yankee
side measurements are obtained, subtract the average initial L reading found
for the unused felts from each of the three Yankee side L readings and each
of the three off-Yankee side L readings. Calculate the average delta for the
three Yankee side values. Calculate the average delta for the three off-
Yankee side values. Subtract the felt factor from each of these averages.
The final results are termed a lint for the off-Yankee side and a lint for the
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Yankee side of the tissue web. By taking a ratio of the lint value on the
Yankee side compared to the value on the off Yankee side, the "lint ratio" is
obtained. In other words, to calculate the lint ratio, the following formula
is
used:
Lint Ratio = Lint Value, Yankee S~~tp
Lint Value, off-Yankee Side
By taking the average of the lint value on the Yankee side and the off-
Yankee side, an ultimate lint is obtained for the entire single-ply tissue
web.
In other words, to calculate the ultimate lint, the following formula is used:
Ultimate Lint = Lint Value. Yankee Side + Lint Value off-Yankee Side
2
F. Measurement of Panel Softness of Tissue Papers
Ideally, prior to softness testing, the paper samples to be tested
should be conditioned according to Tappi Method #T4020M-88. Here,
samples are preconditioned for 24 hours at a relative humidity level of 10 to
35% and within a temperature range of 22 to 40 °C. After this
preconditioning step, samples should be conditioned for 24 hours at a
relative humidity of 48 to 52% and within a temperature range of 22 to 24
°C.
Ideally, the softness panel testing should take place within the
confines of a constant temperature and humidity room. If this is not
feasible, all samples, including the controls, should experience identical
environmental exposure conditions.
Softness testing is performed as a paired comparison in a form similar
to that described in "Manual on Sensory Testing Methods", ASTM Special
Technical Publication 434, published by the American Society For Testing
and Materials 1968 and is incorporated herein by reference. Softness is
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evaluated by subjective testing using what is referred to as a Paired
Difference Test. The method employs a standard external to the test
material itself. For tactile perceived softness two samples are presented ,
such that the subject cannot see the samples, and the subject is required to
choose one of them on the basis of tactile softness. The result of the test is
reported in what is referred to as Panel Score Unit (PSU?. With respect to
softness testing to obtain the softness data reported herein in PSU, a
number of softness panel tests are performed. In each test ten practiced
softness judges are asked to rate the relative softness of three sets of
paired
samples. The pairs of samples are judged one pair at a time by each judge:
one sample of each pair being designated X and the other Y. Briefly, each X
sample is graded against its paired Y sample as follows:
1. a grade of plus one is given if X is judged to may be a little softer
than Y, and a grade of minus one is given if Y is judged to may be a
little softer than X;
2. a grade of plus two is given if X is judged to surely be a little
softer than Y, and a grade of minus two is given if Y is judged to
surely be a little softer than X;
3. a grade of plus three is given to X if it is judged to be a lot
softer than
Y, and a grade of minus three is given if Y is judged to be a lot softer
than X; and, lastly:
4. a grade of plus four is given to X if it is judged to be a whole lot
softer
than Y, and a grade of minus 4 is given if Y is judged to be a whole
lot softer than X.
The grades are averaged and the resultant value is in units of PSU.
The resulting data are considered the results of one panel test. If more than
one sample pair is evaluated then al! sample pairs are rank ordered
according to their grades by paired statistical analysis. Then, the rank is
shifted up or down in value as required to give a zero PSU value to which
ever sample is chosen to be the zero-base standard. The other samples
then have plus or minus values as determined by their relative grades with
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respect to the zero base standard. The number of panel tests performed
and averaged is such that about 0.2 PSU represents a significant difference
in subjectively perceived softness.
G. Measurement of Opacity of Tissue Papers
The percent opacity is measured using a Colorquest DP-9000
Spectrocolorimeter. Locate the on/off switch on the back of the processor
and turn it on. Allow the instrument to warm up for two hours. If the
system has gone into standby mode, press any key on the key pad and
allow the instrument 30 minutes of additional warm-up time.
Standardize the instrument using the black glass and white tile. Make
sure the standardization is done in the read mode and according to the
instructions given in the standardization section of the DP9000 instrument
manual. To standardize the DP-9000, press the CAL key on the processor
and follow the prompts as shown on the screen. You are then prompted to
read the black glass and the white tile.
The DP-9000 must also be zeroed according the instructions given in
the DP-9000 instrument manual. Press the setup key to get into the setup
mode. Define the following parameters:
OF filter: OUT
Display: ABSOLUTE
Read Interval: SINGLE
Sample ID: ON or OFF
Average: OFF
Statistics: SKIP
Color Scale: XYZ
Color Index: SKIP
Color Difference Scale: SKIP
Color Difference Index: SKIP
CMC Ratio: SKIP
CMC Commercial Factor: SKIP
Observer: 10 degrees
Illuminant: D
M1 2nd illuminant: SKIP
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Standard: WORKING
Target Values: SKIP
Tolerances: SKIP
Confirm the color scale is set to XYZ, the observer set to 1 O degrees,
and the illuminant set to D. Place the one ply sample on the white
uncalibrated tile. The white calibrated tile can also be used. Raise the
sample and tile into place under the sample port and determine the Y value.
Lower the sample and tile. Without rotating the sample itself, remove
the white tile and replace with the black glass. Again, raise the sample and
black glass and determine the Y value. Make sure the 1-ply tissue sample is
not rotated between the white tile and black glass readings.
The percent opacity is calculated by taking the ratio of the Y reading
on the black glass to the Y reading on the white tile. This value is then
multiplied by 100 to obtain the percent opacity value.
For the purposes of this specification, the measure of opacity is
converted into a "specific opacity", which, in effect, corrects the opacity
for
variations in basis weight. The formula to convert opacity % into specific
opacity °!o is as follows:
Specific Opacity - (1 - (Opacity/ 100)(1/Basis Weight?~ X 100,
where the specific opacity unit is per cent for each g/m2, opacity is in units
of per cent, and basis weight is in units of g/m2.
Specific opacity should be reported to 0.01 %.
G. Measurement of Strength of Tissue Papers
DRY TENSILE STRENGTH'
The tensile strength is determined on one inch wide strips of sample
using a Thwing-Albert Intelect t1 Standard Tensile Tester (Thwing-Albert
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Instrument Co., 10960 Dutton Rd., Philadelphia, PA, 19154). This method
is intended for use on finished paper products, reel samples, and
unconverted stocks.
SAMPLE CONDITIONING AND PREPARATION'
Prior to tensile testing, the paper samples to be tested should be
conditioned according to Tappi Method #T4020M-88. All plastic and paper
board packaging materials must be carefully removed from the paper
samples prior to testing. The paper samples should be conditioned for at
least 2 hours at a relative humidity of 48 to 52% and within a temperature
range of 22 to 24 °C. Sample preparation and all aspects of the tensile
testing should also take place within the confines of the constant
temperature and humidity room.
For finished product, discard any damaged product. Next, remove 5
strips of four usable units (also termed sheets) and stack one on top to the
other to form a long stack with the perforations between the sheets
coincident. Identify sheets 1 and 3 for machine direction tensile
measurements and sheets 2 and 4 for cross direction tensile measurements.
Next, cut through the perforation line using a paper cutter (JDC-1-10 or
JDC-1-12 with safety shield from Thwing-Albert Instrument Co., 10960
Dutton Road, Philadelphia, PA, 19154) to make 4 separate stocks. Make
sure stacks 1 and 3 are still identified for machine direction testing and
stacks 2 and 4 are identified for cross direction testing.
Cut two 1 " wide strips in the machine direction from stacks 1 and 3.
Cut two 1 " wide strips in the cross direction from stacks 2 and 4. There are
now four 1 " wide strips for machine direction tensile testing and four 1 "
wide strips for cross direction tensile testing. For these finished product
samples, all eight 1 " wide strips are five usable units (also termed sheetsl~
thick.
For unconverted stock and/or reel samples, cut a 15" by 15" sample
which is 8 plies thick from a region of interest of the sample using a paper
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cutter (JDC-1-10 or JDC-1-12 with safety shield from Thwing-Albert
Instrument Co., 10960 button Road, Philadelphia, PA, 19154) . Make sure
one 15" cut runs parallel to the machine direction while the other runs
parallel to the cross direction. Make sure the sample is conditioned for at
least 2 hours at a relative humidity of 48 to 52% and within a temperature
range of 22 to 24 °C. Sample preparation and all aspects of the tensile
testing should also take place within the confines of the constant
temperature and humidity room.
From this preconditioned 15" by 15'° sample which is 8 plies
thick,
cut four strips 1 " by 7'° with the long 7" dimension running parallel
to the
machine direction. Note these samples as machine direction reel or
unconverted stock samples. Cut an additional four strips 1 °' by
7°' with the
long 7" dimension running parallel to the cross direction. Note these
samples as cross direction reel or unconverted stock samples. Make sure all
previous cuts are made using a paper cutter (JDC-1-10 or JDC-1-12 with
safety shield from Thwing-Albert Instrument Co., 10960 button Road,
Philadelphia, PA, 19154). There are now a total of eight samples: four 1 "
by 7" strips which are 8 plies thick with the 7'° dimension running
parallel to
the machine direction and four 1 " by 7°° strips which are 8
plies thick with
the 7" dimension running parallel to the cross direction.
OPERATION OF TENSILE TESTER:
For the actual measurement of the tensile strength, use a Thwing-
Albert Intelect II Standard Tensile Tester (Thwing-Albert Instrument Co.,
10960 button Rd., Philadelphia, PA, 19154). Insert the flat face clamps
into the unit and calibrate the tester according to the instructions given in
the operation manual of the Thwing-Albert Intelect I1. Set the instrument
crosshead speed to 4.00 in/min and the 1 st and 2nd gauge lengths to 2.00
inches. The break sensitivity should be set to 20.0 grams and the sample
width should be set to 1.00" and the sample thickness at 0.025".
A load cell is selected such that the predicted tensile result for the
sample to be tested lies between 25 % and 75 °~ of the range in use.
For
example, a 5000 gram load cell may be used for samples with a predicted
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tensile range of 1250 grams (25% of 5000 grams) and 3750 grams (75% of
' 5000 grams). The tensile tester can also be set up in the 10% range with
the 5000 gram load cell such that samples with predicted tensiles of 125
- grams to 375 grams could be tested.
Take one of the tensile strips and place one end of it in one clamp of
the tensile tester. Place the other end of the paper strip in the other clamp.
Make sure the long dimension of the strip is running parallel to the sides of
the tensile tester. Also make sure the strips are not overhanging to the
either side of the two clamps. In addition, the pressure of each of the
clamps must be in full contact with the paper sample.
After inserting the paper test strip into the two clamps, the instrument
tension can be monitored. If it shows a value of 5 grams or more, the
sample is too taut. Conversely, if a period of 2-3 seconds passes after
starting the test before any value is recorded, the tensile strip is too
slack.
Start the tensile tester as described in the tensile tester instrument
manual. The test is complete after the crosshead automatically returns to
its initial starting position. Read and record the tensile load in units of
grams
from the instrument scale or the digital panel meter to the nearest unit.
If the reset condition is not performed automatically by the
instrument, perform the necessary adjustment to set the instrument clamps
to their initial starting positions. Insert the next paper strip into the two
clamps as described above and obtain a tensile reading in units of grams.
Obtain tensile readings from all the paper test strips. It should be noted
that
readings should be rejected if the strip slips or breaks in or at the edge of
the clamps while performing the test.
CALCULATIONS:
For the four machine direction 1 " wide finished product strips, sum
the four individual recorded tensile readings. Divide this sum by the number
of strips tested. This number should normally be four. Also divide the sum
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of recorded tensiles by the number of usable units per tensile strip. This is
normally five for both 1-ply and 2-ply products.
Repeat this calculation for the cross direction finished product strips.
For the unconverted stock or reel samples cut in the machine
direction, sum the four individual recorded tensile readings. Divide this sum
by the number of strips tested. This number should normally be four. Also
divide the sum of recorded tensiles by the number of usable units per tensile
strip. This is normally eight.
Repeat this calculation for the cross direction unconverted or reel
sample paper strips.
All results are in units of grams/inch.
For purposes of this specification, the tensile strength should be
converted into a "specific total tensile strength" defined as the sum of the
tensile strength measured in the machine and cross machine directions,
divided by the basis weight, and corrected in units to a value in meters.
EXAMPLES
The following examples are offered to illustrate the practice of the
present invention. These examples are intended to aid in the description of
the present invention, but, in no way, should be interpreted as limiting the
scope thereof. The present invention is bounded only by the appended
claims.
EXAMPLE 1
This comparative Example illustrates a reference process not
incorporating the features of the present invention. This process is
illustrated '
in the following steps:
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First, an aqueous slurry of NSK of about 3% consistency is made up
using a conventional pulper and is passed through a stock pipe toward the
headbox of the Fourdrinier.
In order to impart a temporary wet strength to the finished product, a
1 % dispersion of Parez 750° is prepared and is added to the NSK stock
pipe
at a rate sufficient to deliver 1.25 % Parez 750° based on the dry
weight of
the NSK fibers. The absorption of the temporary wet strength resin is
enhanced by passing the treated slurry through an in-line mixer.
The NSK slurry is diluted with white water to about 0.2% consistency
at the fan pump.
An aqueous slurry of eucalyptus fibers of about 3% by weight is
made up using a conventional repulper.
The eucalyptus is passed through a stock pipe to another fan pump
where it is diluted with white water to a consistency of about 0.2%.
The slurries of NSK and eucalyptus are directed into a multi-channeled
headbox suitably equipped with layering leaves to maintain the streams as
separate layers until discharge onto a traveling Fourdrinier wire. A three-
chambered headbox is used. The eucalyptus slurry containing 80% of the
dry weight of the ultimate paper is directed to chambers leading to each of
the two outer layers, while the NSK slurry comprising 20% of the dry weight
of the ultimate paper is directed to a chamber leading to a layer between the
two eucalyptus layers. The NSK and eucalyptus slurries are combined at the
discharge of the headbox into a composite slurry.
The composite slurry is discharged onto the traveling Fourdrinier wire
and is dewatered assisted by a deflector and vacuum boxes.
The embryonic wet web is transferred from the Fourdrinier wire, at a
fiber consistency of about 15% at the point of transfer, to a patterned
forming fabric of a 5-shed, satin weave configuration having 84 machine-
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direction and 76 cross-machine-direction monofilaments per inch,
respectively, and about 36 % knuckle area.
Further de-watering is accomplished by vacuum assisted drainage until
the web has a fiber consistency of about 28%.
While remaining in contact with the patterned forming fabric, the
patterned web is pre-dried by air blow-through to a fiber consistency of
about 62% by weight.
The semi-dry web is then adhered to the surface of a Yankee dryer
with a sprayed creping adhesive comprising a 0.125 % aqueous solution of
polyvinyl alcohol. The creping adhesive is delivered to the Yankee surface
at a rate of 0.1 % adhesive solids based on the dry weight of the web.
The fiber consistency is increased to about 96% before the web is dry
creped from the Yankee with a doctor blade.
The doctor blade has a bevel angle of about 25 degrees and is
positioned with respect to the Yankee dryer to provide an impact angle of
about 81 degrees.
The percent crepe is adjusted to about 18% by operating the Yankee
dryer at about 800 fpm (feet per minute) (about 244 meters per minute),
while the dry web is formed into roll at a speed of 656 fpm (201 meters per
minutes).
The web is converted into a three-layer, single-ply creped patterned
densified tissue paper product of about 18 Ib per 3000 ft2 basis weight.
EXAMPLE 2
This Example illustrates preparation of a filled tissue paper exhibiting
one embodiment of the present invention .
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An aqueous slurry of eucalyptus fibers of about 3% by weight is
made up using a conventional repulper. Cypro 514 M is added to the slurry at
a rate of 0.02% based on the dry weight of the Cypro 514 relative to the
finished dry weight of the creped tissue paper. The treated slurry is then
carried through a stock pipe toward the paper machine.
TM
The particulate filler is kaolin clay, grade WW Fil Slurry , made by Dry
Branch Kaolin of Dry Branch, GA. It is delivered as a slurry at 70% solids
through a stock pipe where it is mixed with an anionic flocculant, Accurac
62,Mwhich is delivered as a 0.3% dispersion in water. Accurac 62 M is
conveyed at a rate equivalent to about 0.015 °~6 based on a the amount
of
solid weight of the flocculant and finished dry weight of the resultant creped
tissue product. The adsorption of the flocculant is promoted by passing the
mixture through an in line mixer. This forms a conditioned slurry of filler
particles.
The agglomerated slurry of filler particles is then mixed into the stock
pipe carrying the refined eucalyptus fibers
The eucalyptus fiber and particulate filler mixture is divided into two
separate flows in approximately equal amounts and directed toward the
papermachine. Each flow stream is then treated with a cationic starch
RediBOND 5320 M which is delivered as a 1 % dispersion in water. The flow
which will ultimately form the Yankee side layer is treated with the starch at
a rate of 0.1 % based on the dry weight of starch and the finished dry
weight of the resultant creped tissue product. The flow which will
ultimately form the off-Yankee side layer is treated with the starch at a rate
of 0.5% based on the dry weight of starch and the finished dry weight of
the resultant creped tissue product. Absorption of the cationic starch is
improved by passing the resultant mixture through an in line mixer. The
resultant slurries are then each diluted with white water at the inlet of
their
respective fan pumps to a consistency of about 0.2% based on the weight
of the solid filler particles and eucalyptus fibers. After the fan pumps
carrying the combination of agglomerated filler particles and eucalyptus
fibers, additional Accurac 62 M diluted to a concentration of about 0.05 ~6
solids, is added to each of the mixtures at a rate corresponding to about
0.065 % based on the solids weight of the filler and eucalyptus fiber.
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A bond inhibiting composition is prepared by melting together a
mixture of equal amounts of Varisoft 134~ and Polyethylene glycol 400 at a
temperature of about 88°C. The melted mixture is then charged into an
agitated water-stream at a temperature of about 66~C to a concentration of
about 2%, based on the Varisoft content. The bond inhibiting composition
is added to one of the eucalyptus and particulate fiber slurry flows such that
it is added to the flow which will ultimately form the layer to contact the
Yankee surface. An amount of the bond inhibiting composition is added to
comprise approximately 0.15 % based on the Varisoft 134° weight
compared
to the dry weight of the finished tissue.
An aqueous slurry of NSK of about 3% consistency is made up using
a conventional pulper and is passed through a stock pipe toward the
headbox of the Fourdrinier.
In order to impart a temporary wet strength to the finished product, a
1 % dispersion of Parez 750~ is prepared and is added to the NSK stock pipe
at a rate sufficient to deliver 1.25% Parez 750~ based on the dry weight of
the NSK fibers. The absorption of the temporary wet strength resin is
enhanced by passing the treated slurry through an in-tine mixer.
The NSK slurry is diluted with white water to about 0.2% consistency
at the fan pump. After the fan pump, additional Accurac 62~, diluted to a
concentration of about 0.05% solids, is added to the mixture at a rate
corresponding to about 0.065 % based on the solids weight of the filler and
the NSK fiber.
The slurries of NSK and eucalyptus are directed into a multi-channeled
headbox suitably equipped with layering leaves to maintain the streams as
separate layers until discharge onto a traveling Fourdrinier wire. A three-
chambered headbox is used. The combined eucalyptus and particulate filler
containing sufficient solids flow to achieve 80% of the dry weight of the
ultimate paper is directed to chambers leading to each of the two outer
layers, while the NSK slurry comprising sufficient solids flow to achieve
20°~
of the dry weight of the ultimate paper is directed to a chamber leading to a
layer between the two eucalyptus layers. The NSK and eucalyptus slurries
are combined at the discharge of the headbox into a composite slurry.
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The composite slurry is discharged onto the traveling Fourdrinier wire
and is dewatered assisted by a deflector and vacuum boxes.
The embryonic wet web is transferred from the Fourdrinier wire, at a
fiber consistency of about 15 % at the point of transfer, to a patterned
forming fabric of a 5-shed, satin weave configuration having 84 machine-
direction and 76 cross-machine-direction monofilaments per inch,
respectively, and about 36% knuckle area.
Further de-watering is accomplished by vacuum assisted drainage until
the web has a fiber consistency of about 28%.
While remaining in contact with the patterned forming fabric, the
patterned web is pre-dried by air blow-through to a fiber consistency of
about 62% by weight.
The semi-dry web is then adhered to the surface of a Yankee dryer
with a sprayed creping adhesive comprising a 0.125% aqueous solution of
polyvinyl alcohol. The creping adhesive is delivered to the Yankee surface
at a rate of 0.1 % adhesive solids based on the dry weight of the web.
The fiber consistency is increased to about 96% before the web is dry
creped from the Yankee with a doctor blade.
The doctor blade has a bevel angle of about 25 degrees and is
positioned with respect to the Yankee dryer to provide an impact angle of
about 81 degrees.
The percent crepe is adjusted to about 18% by operating the Yankee
dryer at about 800 fpm (feet per minute) (about 244 meters per minute),
while the dry web is formed into roll at a speed of 656 fpm (200 meters per
minutes).
The web is converted into a three-layer, single-ply creped patterned
densified tissue paper product of about 18 Ib per 3000 ft2 basis weight.
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EXAMPLE 3
This Example illustrates preparation of a filled tissue paper exhibiting
one embodiment of the present invention .
An aqueous slurry of eucalyptus fibers of about 3% by weight is
made up using a conventional repulper. Cypro 514° is added to the
slurry at
a rate of 0.02% based on the dry weight of the Cypro 514 relative to the
finished dry weight of the creped tissue paper. The treated slurry is then
divided into two equal flows with each flow carried through its own stock
pipe toward the paper machine.
The particulate filler is kaolin clay, grade WW Fil Slurry°, made
by Dry
Branch Kaolin of Dry Branch, GA. It is delivered as a slurry at 70% solids
through a stock pipe where it is mixed with an anionic flocculant, Accurac
62, which is delivered as a 0.3% dispersion in water. Accurac 62° is
conveyed at a rate equivalent to about 0.015% based on a the amount of
solid weight of the flocculant and finished dry weight of the resultant creped
tissue product. The adsorption of the flocculant is promoted by passing the
mixture through an in line mixer. This forms a conditioned slurry of filler
particles.
The agglomerated slurry of filler particles is then mixed into one of the
stock pipes carrying the eucalyptus fibers and the final mixture is treated
with a cationic starch FiediBOND 5320°~ which is delivered as a 1
dispersion in water and at a rate of 0.75 % based on the dry weight of
starch and the finished dry weight of the resultant creped tissue product.
Absorption of the cationic starch is improved by passing the resultant
mixture through an in line mixer. The resultant slurry is then diluted with
white water at the inlet of a fan pump to a consistency of about 0.2% based
on the weight of the solid filler particles and eucalyptus fibers. After the
fan
pump carrying the combination of agglomerated filler particles and
eucalyptus fibers, additional Accurac 62°, diluted to a concentration
of
about 0.05% solids, is added to the mixture at a rate corresponding to
about 0.065% based on the solids weight of the filler and eucalyptus fiber.
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The other stock pipe carrying eucalyptus fibers is diluted with white
water at the inlet of a fan pump to a consistency of about 0.2% based on
the weight of the solid filler particles and eucalyptus fibers. After the fan
pump carrying the combination of agglomerated filler particles and
eucalyptus fibers, additional Accurac 62°, diluted to a concentration
of
about 0.05% solids, is added to the mixture at a rate corresponding to
about 0.065% based on the solids weight of the eucalyptus fiber.
A bond inhibiting composition is prepared by melting together a
mixture of equal amounts of Varisoft 134° and Polyethylene glycol 400
at a
temperature of about 88°C. The melted mixture is then charged into an
agitated water-stream at a temperature of about 66~C to a concentration of
about 2%, based on the Varisoft content. The bond inhibiting composition
is added to the eucalyptus slurry flows such that it is added to the flow
which will ultimately form the layer to contact the Yankee surface. An
amount of the bond inhibiting composition is added to comprise
approximately 0.15% based on the Varisoft 134° weight compared to the
dry weight of the finished tissue.
An aqueous slurry of NSK of about 3% consistency is made up using
a conventional pulper and is passed through a stock pipe toward the
headbox of the Fourdrinier.
In order to impart a temporary wet strength to the finished product, a
1 % dispersion of Parez 750° is prepared and is added to the NSK stock
pipe
at a rate sufficient to deliver 1.25% Parez 750° based on the dry
weight of
the NSK fibers. The absorption of the temporary wet strength resin is
enhanced by passing the treated slurry through an in-line mixer.
The NSK slurry is diluted with white water to about 0.2% consistency
at the fan pump. After the fan pump, additional Accurac 62°, diluted to
a
concentration of about 0.05% solids, is added to the mixture at a rate
corresponding to about 0.065% based on the solids weight of the filler and
the NSK fiber.
The three slurries (NSK, eucalyptus mixed with filler, and eucalyptus
without filled are directed into a multi-channeled headbox suitably equipped
with layering leaves to maintain the streams as separate layers until
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discharge onto a traveling Fourdrinier wire. A three-chambered headbox is
used. The slurry of eucalyptus without particulate filler is directed to the
chamber discharging directly onto the forming wire surface. The slurry
containing the NSK is directed to the center chamber, and the slurry of
combined eucalyptus and particulate filler is directed to the outer layer
chamber away from the forming surface. The NSK slurry comprising
sufficient solids flow to achieve about 20% of the dry weight of the ultimate
paper, the eucalyptus-only slurry comprises sufficient solids flow to achieve
about 36% of the dry weight of the ultimate paper, and the combined
eucalyptus and particulate filler slurry comprises sufficient solids to
achieve
about 44% of the dry weight of the ultimate paper. The slurries are
combined at the discharge of the headbox into a composite slurry.
The composite slurry is discharged onto the traveling Fourdrinier wire
and is dewatered assisted by a deflector and vacuum boxes.
The embryonic wet web is transferred from the Fourdrinier wire, at a
fiber consistency of about 15 % at the point of transfer, to a patterned
forming fabric of a 5-shed, satin weave configuration having 84 machine-
direction and 76 cross-machine-direction monofilaments per inch,
respectively, and about 36% knuckle area.
Further de-watering is accomplished by vacuum assisted drainage until
the web has a fiber consistency of about 28%.
While remaining in contact with the patterned forming fabric, the
patterned web is pre-dried by air blow-through to a fiber consistency of
about 62% by weight.
The semi-dry web is then adhered to the surface of a Yankee dryer
with a sprayed creping adhesive comprising a 0.125 % aqueous solution of
polyvinyl alcohol. The creping adhesive is delivered to the Yankee surface
at a rate of 0.1 % adhesive solids based on the dry weight of the web.
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The fiber consistency is increased to about 96% before the web is dry
creped from the Yankee with a doctor blade.
The doctor blade has a bevel angle of about 25 degrees and is
positioned with respect to the Yankee dryer to provide an impact angle of
about 81 degrees.
The percent crepe is adjusted to about 18% by operating the Yankee
dryer at about 800 fpm (feet per minute) (about 244 meters per minute),
while the dry web is formed into roll at a speed of 656 fpm (200 meters per
minutes).
The web is converted into a three-layer, single-ply creped patterned
densified tissue paper product of about 18 Ib per 3000 ft2 basis weight.
Exam 1e 1 Exam 1e 2 Exam 1e 3
Kaolin content None 8% 9.5%
%
Kaolin Retention N/A 83.2% 96.3%
(Overall)
Tensile Strength 370 370 369
( /in)
S ecific O acit 5.06 5.45 5.27
%
Yankee Side Lint 7.3 9.4 10.5
Off-Yankee Side 7.2 5.5 7.5
Lint
Lint Ratio 1.0 1.7 1.4
Ultimate Lint 7.3 7.5 9.1
Number
Softness score +0.08 +0.56 +0.54
